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NUCLEAR PHYSICS: Chapter 19
Branch of physics that deals with the study of the nucleus is called nuclear physics.
THE NECLEUS:
The central part of an atom having positive charge is called nucleus. It contains protons
and neutrons.
PROTON:
Proton is a positively charged particle present inside the nucleus. Its mass is 91.67x10-27 kg
and its charge is +1.6x1019 kg.
NEUTRON:
Neutron is a neutral particle present inside the nucleus. Its mass is 1.67x1027 kg.
ELECTRON:
Electron is a negatively charged particle revolves around the nucleus in the orbits. Its
mass is 9.1x10-31 kg and its charge is 1.6x10-19 C.
MASS NUMBER:
The total number of protons and neutrons present inside the nucleus is called mass number.
OR
The total number of neutrons present inside the nucleus is called mass number.
i.e. A = Z + N
A = mass number, Z = protons/electrons number, N = neutron number.
CHARGE NUMBER / ATOMIC NUMBER:
The number of protons or electrons present in the atom is called atomic number or
charge number. It is denoted by Z.
NEUTRON NUMBER:
The number of neutrons present in the nucleus is called neutron number. It is denoted
by N
Mathematically it is given as:
N = A – Z
Where N = neutron number, A = mass number.
NEUTRAL RADIOACTIVITY:
Definition:
The spontaneous emission of invisible rays from elements having atomic number
greater than 82 is called radioactivity. The invisible rays are called radioactive rays and
the elements which emit such rays are called radioactive element.
Examples:
Radioactive elements are polonium (z = 84), Radium (z = 88), thorium (z=90) , uranium
(z=92) etc. As the phenomenon is natural, therefore it is termed as natural
radioactivity. It was discovered by Henry Becquerel.
ALPHA, BETA AND GAMMA RAYS:
(Ruther ford’s experiment.)
Ruther ford’s performed an experiment to study the radiations emitted by radioactive
element. A radioactive element for example radium is placed in a cavity made in the
block of the lead. The radiation coming out of the whole in the cavity are allowed to
enter into a vacuum chamber in which magnetic field is applied perpendicular to the
plane of the paper and having direction toward. The charged radiations are deflected
by the magnetic field. Three images are produced on the photographic plate which is
placed in the vacuum chamber straight above the radiations bending towards left are
positively charged radiations and are called Apha () rays. The radiations bending
towards right are negatively charged and are called  rays. The under acted radiations
are neutral.
PROPERTIES OF RADIOACTIVE RAYS:
1. Alpha rays:
i. The are positively charged radiations.
ii. They consist of positively charged helium nuclei, called  particle (2He4)
iii. Each  particle consists of two protons and two neutrons.
iv. Mass of alpha particle is equal to mass of helium nuclei.
v. Charge of apha particle is equal to +2e.
vi. The speed of alpha particle is almost 100 times lesser than the speed of Light.
vii.  rays have low penetrating power.
viii.  rays have high ioizing power.
ix.  rays produce fluorescence in certain substance.
x.  rays show relfection in electromagnetic field.
2. Beta rays:
i. They are negatively charged particles.
ii. They consist of negatively charged particle called electron.
iii. Mass of beta particle is equal to mass of electron.
iv. Charge of each  particle is equal to –1e
v.  rays (electrons) are emitted than the nucleus.
vi. The velocity of a  particle is almost 10 times lesser than the velocity of
Light. (Range: 19x109 m/s to 27x107 m/s)
vii.  rays effect th photographic plate.
viii.  rays have low ionization power.
ix.  rays have high ionization power.
x.  rays produce fluorescence.
3. Gamma rays:
i. γ – rays are neutral ionizations.
ii. Y – rays are electromagnetic waves like x-rays.
iii. Y – rays have wave length shorter than the wave length of x – rays.
iv. Y – rays have frequency greater than the frequency of x – rays.
v. Y – rays have negligible ionization power.
vi. Y – rays have very high penetrating power.
vii. Y – rays producer feeble flourensence.
viii. Y – rays eject electrons when fall on metal.
ix. Y – rays travel with the speed of light.
HALF LIFE OF AN ELEMENT:
Definition:
The deviation in which original number of atom becomes half is called half life of an element. OR
The time in which half of the given number of radioactive atoms, decay into daughter,
is called half life of an element.
Mathematical form:
Mathematically, it is given as:
T1/2 = 0.693/
Where T1/2 = half life  = decay constant
When an element decays by  or  emission if is converted into new element. The new
element is called daughter element and the original element is called parent element.
RADIOACTIVE ISOTOPES:
Definition:
“Element having same atomic number but different atomic masses are called isotopes.”
If one isotope is unstable and emits radioactive rays is called radio isotopes.
OR
“Elements having same proton number but different neutron number and emit  ,  or
 rays are called radioactive isotope.”
EXAMPLE:
I. Carbon has two isotopes 6C12 and 6C14 . 6C14 is unstable are emit  rays.
Therefore it is considered as a radioactive isotope.
II. Hydrogen has three isotopes, 1H1 , 1H2 and 1H3 .
1H3 is radioactive isotopes and emits out  particle.
EINSTEIN ENERGY MASS RELATION:
According to the special theory of relativity, “Energy and mass are interconvert able
mass can be converted into energy and energy can be converted into mass.”
Einstein energy mass radiation is given as
E = mC2
Where, E = energy, m = mass, C = velocity of light.
NUCLEAR REACTION:
DEFINITION:
A reaction which produce certain changes to the nucleus is called nuclear reaction.
NUCLEAR FISSION:
DEFINITION:
The process in which heavy decomposed into lighter nuclei is called nuclear fission or
the phenomenon in which heavy nucleus is broken into two middle order nuclei with
the release of energy is called nuclear fission.
EXAMPLE:
The nuclear fission is given as
92U235 + 0 n1 36Ba144 + 36Kr90 + 3 0n1 + Energy
The energy is released because mass on the right hand is less than the mass on the left
hand side. The difference in mass (loss of mass) is converted into energy.
NUCLEAR CHAIN REACTION:
DEFINITION:
A reaction which once starts repeat itself in the same manner is called nuclear chains reaction.
EXAMPLE:
When 92U235 is bombarded by slow reaction, fission is produced. The three neutrons
released in this fission can be employed to produce fission in three other nuclei of
92U235 and a chain reaction can be developed as shown in figure. If this process is
allowed to continue, then more and more nuclei undergo fission and larger amount of
energy is released. This is called nuclear chain reaction.

TYPES OF CHAIN REACTION:
There are two types of chain reaction:
i. Controlled chain reaction.
ii. Uncontrolled chain reaction.
NUCLEAR REACTORS:
DEFINITION:
A device which is used to perform nuclear chain reaction in controlled manner is called
nuclear reactor.
OR
“A system used to obtain controlled amount of head from nuclear fission is called
nuclear reactor.”
The nuclear chain reaction in uranium releases energy in the form of heart. If the chain
reaction is controlled a constant. How of heat is obtained this heat can be used to run
generator for producing electricity.
The fissionable material 92U235 is fission element. The three neutrons released in each
fission are fast moving. These neutrons must be slowed down because only neutrons
produced fission in 92U235 the process of slowing down of neutrons is called
moderation. In the reactor heavy water is such as moderator.
The chain reaction is controlled by using neutron absorbing rods. Two out of the three
neutrons are absorbed by control rods.
The heat produced in the nuclear reactor is carried away by the circulation of
carbondioxide is the core of reactor. It is used to produce steam and this steam is used
to run the generator for producing electricity.
NUCLEAR FUSSION:
DEFINITION:
The phenomenon in which two light nuclei are combined with the release of energy, is
called nuclear fussion or fussion reaction.
OR
“The process in which two lighter nuclei combines together to heavy. Heavy nucleus is
called nuclear fussion.”
EXAMPLE:
1H2 + 1H3 2He+ + 0n1 + energy
1H2 + 1H2 2He4 + energy.
ENERGY OF THE SUN:
Solar energy from the sun is due to the fusion of hydrogen into helium. This fusion is
fossible because the temperature in the sun is about 1.5x106 C. The fusion reaction
that happens in the sun is given as::
1H2 + 1H2 2H4 + energy
THE ATOMIC BOMB:
The atomic bomb is based on nuclear fission. The maximum amount of mass required
to start the nuclear fission is called critical mass. If the mass is slightly greater than the
critical mass, the chain reaction will develop at a faster rate and in a very short time
tremendous amount of energy will be released. This producer is adopted in atomic
bomb.
THE HYDROGEN BOMB:
The hydrogen bomb is based on the principle of nuclear fission. To start fission
reaction, a very high temperature is nucleated. This high temperature is obtained from
fission chain reaction.
The energy released in the explosion of hydrogen bomb is far greater than that
released from the explosion of an atom.
USES OF RADIO ISOTOPES:
The isotopes of an element which emits out radiation is called radio isotope. Radio
isotopes are widely used in
i. Agriculture
ii. Medicine etc.
I INDUSTRY:
A Radio isotopes are used to check the thickness of the material being produced.
B Radio isotopes are used to detect cracks in welded joints.
C Radio isotopes are used to detect the leakages in pipes.
II AGRICULTURE:
A Varieties of seeds for various agriculture commodities which show resistance
against the attacks of pets have been produced after imitation through
radiations from radio isotopes.
B Radiation from radio isotopes are used to kill bacteria and preserve food stuff.
C It is used to determine the optimum amount of fertilizers and other nutrient
intake by plants. Its count rate is used to determine the amount of chemicals
absorbed by various parts of the plants.
III MEDICINE:
A Radio isotopes iodine 131, is used to study thyroid glands.
B Radio isotopes phosphorus 32 is used to locate the position of tumor in the
brain.
C Radio isotope strontium is used in the treatment of internal wounds.
D Radio isotope sodium is used tracing the blood circulation in the body.
E Radio isotope phosphorus has found effective for heating leukemia as radiation
emitted by Hood cancer if destroys the excess production of white blood corpuscles (cells).
F Radio isotope cobalt – 60 is used to treat cancerous tumors inside the body RADIATION HAZARDS:
In contrast to good use in industry, agree culture medicine etc. nuclear radiations are very
dangerous to the human body. They can damage the body cells due to the ionization which
they produce. A body, if strongly heated suffers the following diseases.
i. Anemia (a decrease in red blood corpuscles).
ii. Leukemia (an increase in white blood corpuscles)
iii. Malignant tumors.
iv. Cataracts (eye lens becomes opaque).
RADIATION SAFETY:
(Precautions to minimize radiation danger)
i. One should be at a safe distance from radio isotopes.
ii. The time for radiation exposure should be short.
iii. The radiations from nuclear reactor are shielded by the thick concrete walls.
iv. The radioactive material should be kept in lead box with the lid made of lead.

Electronics: Chapter 18 X Physics,03362023305, Edexcel, IGCSE, Physics tuition karachi

Q1. What do you mean Electronics?
Ans: ELECTRONICS:
It is that branch of Physics which deals in the structure and analysis of devices which
emit electrons. In electronics, uses and flow and controlling of those devices are
studied. Additionally which circuit designed for emitting, flow and control of electrons
are called Electronic circuits.
Q2. Give application of electronics in every day life.
Ans: Applications of electronics in every day-life are as follows:
(i) Radio (ii) TV (iii) Motion Pictures Iiv) Computers (v) VCR
APPLICATION IN MODERN ELECTRONICS:
(i) Automatic Washing Machine (ii) Microwave oven
(iii) Robots (iv) Telephones (v) Pocket Calculator.
Q3. Define Insulator and Semiconductor.
Ans: INSULATOR:
Those things which do not conduct electricity or which do not posses, free electrons
are called insulator. For example, Non-metallic objects as Gases and liquids.
SEMICONDUCTOR:
Those things which possess intermediate qualities between conductor and non-
conductor, like IVA group elements. When Carbon or Germenium or Silicon is
combined with Randium, then the mixture possess free-electrons and these electrons
are responsible for the flow of electric current.
Q4. What are P-type materials?
Ans: P-TYPE METRIAL:
Germinium and Silicon like elements possess four electrons in then outermost shell. If
any atom is mixed with such atoms. Who possess three electrons, then three electrons
from each side will make a covalent bond but an incomplete one. Because Germinium
and Silicon need four electrons in the outermost shell. Therefore, the substance made
from the mixture of Germinium and Silicon with Randium would possess greater
amount of positive charges. Hence the material which possess positive charges, is
called P-type material.

Q5. Define N-type material.
Ans: N-TYPES:
If an atom of five electrons, is mixed with crystal of Germinium and Silicon, for example
Arsenic. Then four electrons will form convalent bond and one electron will remain free
Since this material possess negative charges, therefore it is called N-type material.
Q6. Differentiate between N-type and P-type.
Ans:
N – TYPE
1. It is formed when Germinium like, atom Is combined with Arsenic like atom having 5+ ve valency.
2. It has excess of negative charge.
3. Conductivity is produced because of
one additional electron.
4. This is semiconductor. P – TYPE
1. It is formed when Germinium like atom is mixed with Inidium like atom having
3 + ve valency.
2. It has excess of positive charge.
3. Conductivity is produced because
Less electrons.
4. This also a semiconductor.
Q7. What is P-N junction ?
Ans: P-N JUNCTION:
When a block of P-type element is placed with block of N-type element then their
mutual boundary is called P-N junction and device formed is called Semi diode.
If a P-N junction, concentration of free electrons is high in N-type where as P-type
element has concentration of holes. Now P-type elements diffuse free-electrons in
matter and holes diffuse in N-type. Hence, this junction is known as P-N junction.

Q8. Prove how does P-N diode work.
Ans: P-N JUNCTION AS A DIODE:
When a P-N junction is joined with a battery in such manner that P-type material is
connected to positive terminal and N-type is joined with negative potential, then
positive terminal pulls the whole P-type and negative terminal will repel the electrons.
Now current will flow around the junction. If negative terminal is connected with P-
type and positive terminal is with N-type then negative potential attract the holes and
positive terminal will attract the electrons. Therefore, no current will passes across the
P-N junction. This proves that current passes in one direction in P-N junction and same
ss in diode. Hence diode works as P-N junction.
Q9. What is diode?
Ans: DIODE:
This consists of two electrodes placed in a high standard glass tube. That is why it is
called Diode. Among two of them, one electrode is made by a tungsten filament
coated with metal e.g. Barium Oxide or Strancium, which is called Cathode. The other
electrode consists of a Nickel plate which is called Anode. When filament is heated, it
emits electrons and makes an electron-cloud around the cathode. When positive
potential is supplied to positive anode, then it attracts the electrons and hence current
is passed.
Q10. Define hole, Thermonic emission and Doping.
Ans: HOLE:
When atom like Indium is mixed with atom like Silicon then three electrons of Indium
make covalent bond with three electrons of Silicon and one electron remains alone.
Hence, covalent bond is not a complete one because of that single electron and a
place remains vacant. Ths vacant place is called Hole.
THERMONIC EMISSION:
Such process in which a cathode of diode emits electrons on heating is known as
thermonic emission.
DOPING:
It is a process in which an element is made semiconductor P-type and N-type by mixing.
Q11. Define Forward Biased.
Ans: FORWARD BIASED:
When a P-N junction is joined with a battery
in such a manner that its P-type is connected
with positive terminal and N-type with negative
terminal, then current will flow this phenomenon
is known as Forward Biased. The Potential
produces an electric field, due to which resistance
in height of junction falls down. Since the height of
potential resistance is 0.7 to 0.1, therefore an increase
in Potential will vanish the resistance and resistance
falls down to zero and current flows in circuit.
Q12. Explain Reverse Biased.
Ans REVERSE BIASED:
When a P-N junction is joined with a battery
in such a way that its P-type is connected to
negative terminal and N-type is connected
with positive terminal then a reverse potential
creates an electric field which acts in the
direction of field of Potential resistance.
Therefore, a powerful field produces on the
junction. And height of resistance raises.
The high of resistance resists against the flow
of electrons. Hence, no current flows. This whole
process is known as Reverse Biased.
Q13. What is meant by Rectification?
Ans: RECTIFICATION:
The process, in which D.C is changed to AC, is called Rectification. The producting
current is used for charging battery and plating. Usually semiconductor is used for this
purpose. The device which converts AC to D.C is called Rectifier. There are two types of
rectifier.
i. Half-wave Rectifier
ii. Full-wave Rectifier
Q14. Explain Half-wave rectifier.
Ans: HALF- WAVE RECTIFIER:
Wave of current always consists of
two parts. One part is positive and
other one is negative.
Only positive part conducts A.C in
half-wave rectifier where as negative
charged does not . Consider the given circuit Diode and Resistance are connected
parallel and transformer is also connected parallel to them. When diode passes the
current during half positive round, where as stops the half negative round. Hence
there is only one direction for flow of current.
Q15. Give complete structure of Complete wave Rectifier.
Ans: COMPLETE WAVE RECTIFIER:
In this process, A.C conducts with both parts
of voltage, which consists of two parts. This
process is performed with two diodes which
alternately work for each other.
One diode provides current to load during half
positive cycle of voltage where as the other does
the same thing in next half cycle of voltage.
Hence current flows only in one direction.
Therefore, complete wave rectifier uses both half
cycles of voltage to provide DC output.
Q16. Diode works as Rectifier. Explain.
Ans: DIODE AS A RECTIFIER:
Such device which change A.C voltage in DC are called Rectifiers and Phenomena is
called Rectification

Voltage is supplied as Input, which is rectified necessarily. During positive half cycle, P-
type of diode is positive, holes are pulled towards junction. Hence resistance of
junction falls and current flows in the circuit . It becomes negative in other negative half
cycle and holes pulled away from junction. Now resistance of junction raises and no
current flows. So, it is proved that Diode only allow to pass positive cycle, means that
Diode works as a Half-wave Rectifier.
Q17. What are Transistors? How many types of transistors are?
Ans: TRANSISTORS:
Word “Transistor” is composed of two words, one is “Transformer” and other is
“Resistor”.
Schematic construction
p-type Collector n-type Collector
n-type Base p-type Base
p-type Emitter n-type Emitter
pnp npn
It is a semiconductor device which consists of three electrolytes. First one is “BASE”.
second is “Emitter” and third one is “Collector” . Detail of their wok is as follows:
BASE:
It is central parts of the transistor which separates the collector and emitter.
EMITTER:
This part supplies charges.
COLLECTOR:
This part of transistor receives charges.
TYPES OF TRANSISTORS:
i. N.P.N.Types transistors:
In this type of transistor, layer of P-type is placed between two parts of N-types
of material. Central part is called Base, other two parts are Emitter and Collector
respectively.
ii. P. N. P Type Transistors:
P.N.P type transistor consists of N-type material sandwiches between two P-
type materials Central core is called Base, and other two are Collector and
emitter respectively.
Q18. How transistors work?
Ans: WORKING OF TRANSISTORS:
There are two paths for the flow of current in transistors.
i. Base Emitter path where transistors receive current.
ii. Collector emitter path from where current is received from transistors.
Q19. How does an transistor work as an Amplifier?
Ans: TRANSISTOR AS AMPLIFIER:
Amplifier means an accumulator of transistor, if amount of current is increased
in Base, quantity of current reaches maximum in Collector such maximization of
current shows that transistor has qualities of an amplifier.

NPN Transistor Amplifier

USES OF TRANSISTORS:
Transistor is used in following apparatus.
i. Radio ii. Television (iii) Computer
iv. Telephone Set. (v) Stabilizers voltage (vi) VCR
Q20. What do you mean by Electromagnetic Waves?
Ans: ELECTROMAGNETIC WAVES:
Such waves which are produced when magnetic and electric field make a right angle in
a vibrating state are called Electromagnetic Waves. They do not need any medium to
transportation. Examples are light waves Radiowaves, Ultraviolet waves etc.
Q21. Explain Telecommunication.
Ans: TELECOMMUNICATION:
The branch of Physics which studies the production and uses of radial waves of
different frequencies, transporting audible and visual impression, is called
Telecommunication. Following devices works as telecommunication devices
i. Telephone
ii. Telegraph
iii. Radio
iv. Television
Q22. Write the names of parts used in Telegraph.
Ans: Basically, there are two parts in Telegraphy.
i. Electric bell. ii. Transmitter
i. Electric Bell:
It consists of following parts.
a. Electric magnet:
It is connected with a metal strip by the help of a small spring on
opposite hole.
b. Metal Strip:
A metal strip which based on a support.
ii. Transmitter:
It consists of a metal strip, also called Taping Key connected to a battery. On
pressing it, receiver produces round.
Q23. How telegraphing machine work?
Ans: TELEGRAPHY:
A battery is connected with a tapping key. The other end of tapping key is connected
with an Electromagnet. One end of receiver is joined with earth and while a terminal of
battery is connected to earth. Here, earth works a conductor. In telegraphy messages
are consist of dot and dash like codes. These messages press tapping key. The short
interval between pressings of key is called dot and long interval is known as dash.
When tapping key is pressed, then electric current passes through the coil of
electromagnet and this electromagnet attracts the bar. Due to this attraction electric
Circuit is disconnected and current stops its flow. Now the attraction vanishes and
spring takes the bar back to contact point and current starts flowing. Hence with the
press of tapping key the iron bar vibrates and produces buzzing sound which are
received in the form of message by Morse Code..

Q24. Give the structure and working of Telephone.
Ans: STRUCTURE OF TELEPHONE:
Telephone consists of two parts.
i. Carbon microphone,
ii. Airphone
The lines coming from Exchange are
connected to these two parts Likely,
There are two lines in telephone which
work for the communication A battery
in Exchange supplies current to these lines.
WORKING:
Carbon microphone consists of a sensitive diaphragm. There are packed granules of
carbon in front of diaphragm, Diaphragm vibrates when a contraction or expansion
occurs in these granules. When voice of speaker strikes diaphragm, it also fluctuates.
Similarly, there is a constant magnet placed in earphone which is connected with two
soft cores.
TRANSMISSION OF MESSAGE:
When a person speaks in front of microphone, due to compression and rarefaction in
sound waves the diaphragm tends to vibrate. When the diaphragm is compressed,
granules of carbon also compress and inter-granule distance decreases.. With decrease
in distance, resistance lowers in flow of current, and current fluctuates due in the form
of sound waves.
RECEPTION OF MESSAGE:
When current fluctuate in the form of electric current, it passes through the
electromagnetic waves of receiver and disturbs these waves. Due to this, a plate
in front of electromagnet experiences a force on it. These fluctuations are
transformed into sound waves and receiver hears the sound.

Q25. How does the radio propagate sound?
Ans: RADIO:
First, the voice of speaker is formed in front of speaker. This sound produces
fluctuation in microphone, then these sound waves are converted into
Electromagnetic waves. These electromagnetic waves are amplified by an amplifier.
These amplified waves are transported to transmitter which converts them into Radial
waves. Now these radial waves are transmitted to radio sets with the help of powerful
devices. Where these waves strike with the antenna of radio set and then converted
into alternating current Amplifier placed in radio set, amplifies these waves and
transfers towards the loud speaker. Loud speaker works as a headphone and
electromagnetic waves are heard in the form of sound waves.

Q26. How Television transmits picture? Give the principle of Colored Transmission.
Ans: There are two types of TV transmission.
i. Black and White Transmission. ii. Colour Transmission.
BLACK AND WHITE TRANSMISSION:
The picture of persons, in a program, is taken with the help of a particular camera.
These pictures are converted into electromagnetic waves. Now, these waves are
amplified with the help of an amplifier. These amplified waves are transformed into
radial waves with a transmitter, so that these waves can reach the television set
located in remote regions.
In TV set, these radial waves are transformed into electromagnetic waves. Then
these waves are mobilized to Electron gun with the help of amplifier. This electron
gun fires them in the form of rays on the television screen where they form a picture.
COLOUR TRANSMISSION:
A camera consists of three or four tubes is used in colour transmission. These tubes
resolve a picture into colour component. Then, these colors pictures are converted
first into electromagnetic waves and secondly in radial waves. These radial waves
are transmitted to TV Sets with the help of transmitter where they form a picture onTV Set..
Q27. What do you mean by Sound Recording System?
Ans: SOUND RECORDING SYSTEM:
Sound recording system means to record or capture sound. When voice of person
strikes to microphone, then microphone converts it into fluctuating current. This
fluctuating current is amplifier by a transistor and transferred to a magnetic heat.
This head is called Recording Head. A plastic tape coated with magnetizable
material of Ferric Oxide and Chromium oxide, is placed in front of recording head.
Magnetic field varies with fluctuating current which magnetize the different parts of
tape and sound is recorded in a magnetic pattern on the tape.
Q28. What is Radar?
Ans: RADAR:
Radar, intuitively means to defect and find range of an object with radial methods
radar is large used for the war purposes. This device works as guidance for
aeroplanes and sea-ships on airports and sea-ports respective.
STRUCTURE OF RADAR:
Radar consists of a transmitter receiver
and other several indicating devices
electromagnetic waves of high frequency
i.e. more than 600 MHz produced from a
transmitter which are sent in required
direction with the help of a concave
antenna of radar. When these waves strike
a body, they reflect back with this reflection,
we can detect and find range of a body.
These waves travel with velocity of light.
USES OF RADAR:
i. Radar is used for the forecasting of weather, tornadoes and aviation.
ii. It is used to locate the track of satellite, and for military purpose on land
and sea.
Q29. How does a satellite transmit?
Ans: SATELLITE:
Satellite is a spherical object which consists of different device it suspends in a
particular position of space several satellites are revolving around the earth in their
orbits. Satellite is mainly used for the communication purposes. It is necessary to
remain static relative to earth, in order to match the orbital velocity of satellite with
the spinning velocity of the earth solar power is used in satellite nuclear energy is
also used for this purpose.
TRANSMISSION FROM SATELLITE:
Due to high power, satellite receives signals from an object or a body. Then it amplifies
these signals and transmits these amplified signals towards a particular part of the
earth where these amplified signals are received by TV and Radio etc. On earth, these
signals are received with the help of Dishes, Feed-harms and Satellite receivers. We
often see games, news, and other world affair from other distant parts of the world by
this principle.

Magnet and Electromagnetism: Chapter 17

Physics tutors.

DEFINITION:
A substance having ability to attract magnetic materials is called magnet. The
properties related to magnet are called magnetism.
MAGNET POLES:
Whenever a magnet is suspended freely, it comes to rest with one end facing north
and the other end facing south. The end facing north is called North Pole (N) of the
magnet and the end facing south is called South Pole (S) of the magnet. It is found that
South Pole of one magnet attracts the north pole of other magnet and the north and
south pole of one magnet repel the north and south pole of another magnet
respectively. Thus it can be said that “like pole repel each other and unlike pole attracts
each other.”
MAGNET FORCE:
If the pole of two magnets is brought closer to each other, than a force is found to be
present between them. The force is repulsive if the poles are like and attractive if the
poles are unlike. This force is called magnetic force. It is also found that, “the force
decreases square times with the increase of the distance between the poles and it
increases with the increase of the strength of the poles.”
MAGNETIC FIELD:
The region around the magnet in which it attracts any magnetic material is called
magnetic field.
Or
The region in which magnet can exert its magnetic force is called magnetic field.
MAGNETIC FIELD OF EARTH:
A freely suspended magnet points north
and south because it is under the influence
of earth’s magnetic field. The earth behaves
like a bar magnet having its north pole towards
geographical south and the south pole towards
geographical north.
MAGNETS AND MAGNETIC MATERIALS:
MAGNET:
A substance having ability to attract magnetic substances is called magnet.
MAGNETIC SUBSTANCES:
The substances which are attracted by magnets are called magnetic substances.
For example:
Iron, Cobalt, nickel etc.
NON-MAGNETIC SUBSTANCES:
The substances which neither attracted nor repelled by a magnet are called non-
magnetic substances.
For example: Wood, glass, paper etc.
FERROMAGNETIC SUBSTANCES:
A substance which behaves like a magnet in the presence of strong magnetic field is
called ferromagnetic substances.
For example: Soft iron.
METHODS OF MAKING MAGNET:
Following are the two main method of making magnet.
1. SINGLE TOUCH METHOD:
Consider a steel rod placed on a horizontal
table as shown in figure. The steel rod is
rubbed by the north pole of the bar magnet
which is in the inclined position. Each time
when the bar magnet reaches from N to S,
it is lifted and again to brought to N. This
process is repeated till the steel bar is turned
into magnet.
2. ELECTRICAL METHOD:
A U shaped steel bar is wound with an
insulated copper wire. The two arms are
wound in the opposite direction if the
current is now passed through the wire
for few second. The steel bar becomes a
permanent magnet. In the similar way an
iron or steel bar can be magnetized by
the placing inside the current carrying solenoid.

DEMAGNETIZATION:
Definition:
The process which removes the magnetic properties from the magnet is called
demagnetization.
Following are the methods used for demagnetization.
i. By hammering the magnet when they are pointing in east west direction.
ii. By heating the magnet strongly.
iii. By passing alternating source through the magnet when it is placed in side east west direction.
MAGNETIC EFFECT OF CURRENT:
When current passes through any conductor it
becomes magnet and a magnetic field develops
around it. The strength of magnetic field is directly
proportional to the amount of current flowing
through the galvanometer and inversely proportional
to the distance around it.
The direction of magnetic field can be determined by using write hand rule which is given as;
“If the direction of thumb of right hand indicates the direction of the flow of
current, then the core of the fingers gives the direction of the magnetic field.”
When two current carrying conductors are placed parallel to each other and if the
direction of flow of current in both wire is same then both repel each other and if the
directions are opposite them both attracts each other.
MAGNETIC FIELD DUE TO SOLENDIOD:
Definition:
A long coil of insulated copper wire in the
form of cylinder is called solenoid.
if the current is passed through solenoid,
a very strong magnetic field is produced
inside it. The magnetic field outside the
solenoid is very weak.
ELECTROMAGNETISM AND THEIR APPLICATIONS:
Definition:
When current pass through any conductor it becomes magnet or a magnetic field
develops around it this process is called electromagnetism.
Electromagnets are used in electric bells, telephones receiver, loud speaker, electric
fans, etc.
ELECTRIC BELL:
Definition:
It is an electromagnetic instrument used to produce sound.
Construction:
It is an electromagnetic of electric bell is shown in
the figure. One end of the coil of the coil of
electromagnet is connected to the terminal T1
of the bell and the other end to a screw which
is mounted on an iron strip called armature. A
rod carrying a hammer at its end is attached to
the armature. A very light spring is attached to
the contact adjusting screw. The contact adjusting
screw is connected to terminal T2 of the bell. A
battery and push button are connected to the
terminals T1 and T2 of the bell.
Working:
When the push button is pressed, the circuit is completed and current flows through
the coils of electromagnet. The electromagnet is magnetized and attracts the armature.
Due to which the hammer strikes the bell when the electromagnet attracts the
armature, the armature looses contacts with the screw and current stop flowing due to
which the electromagnet gets demagnetized. The spring bring back the armature in
contact with the screw and the current is again completed. The whole process is
repeated again and again so long as the push button in pressed position and the bell
continuously rings.
TELEPHONE RECEIVER:
The telephone receiver consists of a permanent
magnet which is in contact with two soft non
cores having coil wound on them in the opposite
sense. The two soft iron cores from an electromagnet.
A diaphragm made of magnet alloy is fixed in front of
the electromagnet. The message coming from
transmitting end has variation in current caused by the
variation in sound spoken there. This current when passes through the coil of the electromagnet
the electromagnet is magnetized and the pulling force acts on the diaphragm. Due to variation in
current magnetic strength and the magnetic force diaphragm vibrates and give rise to sound.

ELEVATED TRAIN:
The rolls of elevated train are made of electromagnets in series on the ground. These
are other electromagnets attached to the lower side of the train. Due to the strong
repulsive force between these magnets elevated trains moves.

FORCE ON A CURRENT CARRYING CONDUCTOR IN A
MAGNETIC FIELD:
When a current carrying conductor is placed inside the magnetic field. Magnetic field
exerts magnetic force on it. The force acting on the conductor was studied by Faraday.
It is found that:
i. The current carrying conductor experiences force when it is placed at certain
angle with the magnetic field.
ii. The force acts perpendicular to the direction of current and the magnetic field.
iii. The magnitude of force is proportional to the current and the magnetic field
strength.
iv. The direction of force is found by a rule, called right hand rule which is given as:
‘The thumb is place in the direction of conventional of magnetic field. The
direction in which the palm would push gives the direction of force.

GALVANOMETER:
Definition:
An instrument which is used for detection and measurement of small amount of
current is called galvanometer.
TYPES:
There are two types of galvanometer.
i. Moving coil galvanometer.
ii. Moving magnet galvanometer.
MOVING COIL GALVANOMETER:
A galvanometer in which coil rotates while magnet remains at fixed at its position is
called Moving coil galvanometer.
MOVING MAGNET GALVANOMETER:
A galvanometer in which magnet rotates while coil remains fixed at its position is called
moving magnet galvanometer.
MOVING COIL GALVANOMETER:
Definition:
An instrument in which coil rotates while magnet remains fixed and used for the
detection of current called moving coil galvanometer.
CONSTRUCTION:
It consists of following part.
PERMANENT MAGNET:
A permanent horse shoes magnet with curve poles is used.
ARMATURE:
A rectangular coil is would on a light frame with a pointer at the top of the coil is
pivoted between the poles of a horseshoe magnet.
HAIR SPRINGS:
At the both ends of the coil hair springs are attached which not only act to provide the
path for the current to pass through the coil and also responsible to bring the coil back
to its position when the current is switched off.
WORKING:
When current passes through the coil, the two sides of the coil which are parallel to the
magnetic field no force but the two sides which are perpendicular to the magnetic
experience equal force in the opposite direction. Due to this force the coil rotates and
pointer at the top of the coil moves over a scale. The force acting on the coil depends
upon.
i. The strength of current.
ii. The strength of magnetic field.
iii. The number of turns in the coil.
The movement of the coil gives the amount of work.
AMMETER:
Definition:
An instrument which is used to measure llarge amount of current is called ammeter.
CONVERSION OF GALVANOMETER TO AMMETER:
A galvanometer can be converted into ammeter just by connecting a low resistance in
parallel combination with the galvanometer the low resistance connected in parallel is
called shunt resistance.
VOLTMETER:
Definition:
An instrument which is used to measure potential difference is called voltmeter.
CONVERSION OF GALVANOMETER TO VOLTMETER:
A galvanometer can be converted into voltmeter just by connecting a high resistance
in series combination with the galvanometer.
SIMPLE ELECTRIC MOTOR:
Definition:
An electrical device is used to converts electrical energy to mechanical energy is called
simple electric motor.
It is based on the principle of electromotor.
The speed of rotation of motor depends upon.
i. The magnitude of current through coil.
ii. The strength of magnetic field.
iii. The number of turns in the coil.
ELECTRIC MOTOR:
Definition:
A device which converts electrical energy into mechanical energy is called electric motor.
PRINCIPLE:
It is based on the principle of electromagnetism and force exerted by the magnetic
field on a current carrying coil when it is placed, inside the magnetic field.
CONSTRUCTION:
A coil ABCD is placed between the poles of a magnet. The ends of the coil are
connected to a ring splitted into two halves. Each end is connected to each half of the
ring. The ring splitted into two halves is called commutator.
Two carbon rods, called brushed remain in touch with commutator segments.
WORKING:
First consider the coil is in the horizontal position. When the coil is connected to a
battery, current flows, through it. According to right hand rule, a force acts on the side
BC upward and an equal force acts on the side AD downward. Due to these forces the
coil rotates anti-clock wise. To keep the rotation in one direction, the direction of the
current should change its direction after every half rotation. This is achieved by the
action of commutator. Brushes remain connected the negative and positive
commutator. The speed of the rotation of motor depends upon.
(i) The magnitude of current through the coil.
(ii) The strength of Magnetic field.
(iii) The number of turns in the coil.

Electricity:Chapter 16, X Physics, 03362023305, Edexcel Physics tutor karachi IGCSE Cambridge

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1 ELECTRIC NATURE OF MATTER:
The electric nature of matter means the ability of a matter to produce charge on it. The
addition or the removal of electrons from any atom produces charge on it.
Therefore, charge is defined as:
“The access or the deficiency of electrons.”
There are two types of charge.
i. Positive charge
ii. Negative charge
I POSITIVE CHARGE:
The efficiency or the loss of electrons from any atom creates positive charge on it.
II NEGATIVE CHARGE:
The excess or the addition of electrons in an atom creates negative charge on it.
amount of electron lost by one atom is equal to the number of electrons gained
by another atom. It means that total amount of charge always remains
conserved.
2. COULOMB’S LAW:
STATEMENT:
“ Every two like charges repel each other while unlike charges attract each other with
a force called coulombs force. This force is directly proportional to the product of the
magnitude of the charges and inversely proportional to the square of the distance
between them.”
MATHEMATICAL FORM:
Consider two charges of magnitudes “q1 “ and “ q2 “ at a distance “ I “ from each other.

According to the first part of the law, “Coulomb’s force is directly proportional to the
produce of the magnitude of the charges.”
i.e. F  q1 q 2 ……..1
According to the second part of the law, “Coulomb’s force is inversely proportional to
the square of the distance between them.”
i.e. F  1 ………..2
I 2
Combining 1 and 2
i.e. F  q1 q 2
I 2

When K = coulomb’s constant.
= 9 x 109 Nm2 / C2
Which is the required mathematical form of coulomb’s force.
But coulomb’s constant is given as
K = 1
4Eo
Substitute above relation in the expression of coulomb’s force.
Where, Eo = permittivity of free space. = 8.85 x 10-12 C2 / Nm2
The tendency of a medium to allow the electric effect to pairs through it is called
permittivity.
UNIT OF CHARGE:
The unit of charge is coulomb(c)
 F = K q1 q2
I 2
F = 9 x 109 Nm2 / C2 1C 1C
I m2
When two identical charges separated by 1m repel each other with a force of 9 x 109 N
than it is said that there is a charge of IC on each.
POTENTIAL DIFFERENCE:
Amount of work required to move IC charge is called potential difference.
OR
Work done per unit charge is called potential difference.
OR
The difference of the potential at the terminals of the battery is called potential
difference.
It is denoted by “V” and its unit is volt.
ELECTRIC POTENTIAL (v):
Work done per unit charge against the electric field is called electric potential.
OR
Amount of work required to move IC charge against the electric field is called electric
potential.
MATHEMATICALLY:
V = W / -q
Its unit is volt (v) V = W / q
IC = IJ
IC
It shows that,
If IJ of work is required to displace IC charge than it is said that there is an electric
potential of IV.
ELECTRIC FIELD:
The area or space around a charge (source charge) in which it can produce effect on
any another charge (test charge) is called electric field.
If the charges are of same nature than effect will be repulsive and if the charges are of
opposite nature than effect will be attractive.
ELECTRIC INTENSITY:
The strength of electric field is called electric intensity.
OR
The force exerted by the same charge on a unit test charge is called electric intensity.
MATHEMATICALLY FORM:
Mathematically it is given as:
E = F /q
Its unit is N/C
a. E = F / q
IN / C = 1N
1e
If one neutron force acting on a charge of 1e than it is said that there is N/C.
CURRENT:
The amount of charge flows through a conductor in a unit time is called electric current.
OR
The rate of flow of charge is called electric current.
MATHEMATICAL FORM:
Mathematically it is given as:
Current = charge
Time I = Q / - t
UNIT:
Its unit is ampere (A)
 I = Q / t
1A = IC
IS
It shows that:
“ It one coulomb charge flows through a conductor in 1 sec than it is said that there is a
current of 1A.”
DIRECTION:
Since, current is due to the flow of electrons therefore, it has direction from negative to
positive but in order to produce similarity in the direction of all electrical quantities the
direction of current is conventionally consider from “Positive To Negative “.
CONVENTIONAL CURRENT:
The current having the same magnitude as that of the electric current but has direction
from positive to negative is called conventional current.
OHM’S LAW:
Statement:
Amount of current laws through the conductor is directly proportional to the potential
difference applied at the end of the circuit. Keeping the physical state of the conductor
remains same.
MATHEMATICAL FORM:
If current “ I “ is flowing through the conductor due to potential difference (v) then
Mathematically Ohm’s law is given as: I  V
I = KV ………..1
Where, K = conductance,
It is defined as.
The property of conductor which famous the flow of current through it.
But conductance is reciprocal of the resistance.
i.e. K = L …………..2
R
Where “R” is the resistance and it is defined as, “The opposition offered by the
conductor to resist the flow of current. “
Substituting (2) in (1) I = L- V
R
IR = V
Which is the required mathematical form of Ohm’s law.
COMBINATION OF RESISTOR IN SERIES CIRCUIT:
The combination of resistors in which path for the flow of current is only one is called
series combination.
CHARACTERISTICS:
i. Path of the flow of current is only one.
ii. Current remain same in each resistor.
iii. Potential difference is divided among all resistors.
iv. Sum of all potential difference across each resistor is equal to the potential
difference of battery i.e. V = V 1 + V 2 + V 3
v. Equivalent resistor is equal to the sum of all resistance connecting series i.e.
Required = R 1 + R 2 + R 3
PROOF:
Consider three resistance R 1, R 2 and R 3 connected in series using Ohm’s law.
V = IR
Apply to all resistance At R 1 = V 1 = IR 1
At R 2 = V 2 = IR 2
At R 3 = V3 = IR 3¬
Replace all three resistance by a single resistance “Req” keeping the potential
difference remains same.
From the characteristics of series combination. V = V1 + V2 + V3
Substituting the value:
I req = R1 + R2 + R3
I req = I (R1 + R2 + R3)
This is the required expression.
COMBINATION OF RESISTOR IN PARALLEL CIRCUIT:
The combination of resistors in which path for the flow of current is more than one is
called parallel combination.
CHARACTERISTICS:
i. Path for the flow of current is more than one.
ii. Current is divided among all resistors resistor.
iii. Sum of all currents is equal to the total current supplied from the main source.
I = I1 + I2 + I3
iv. Potential difference remains same across each resistor.
v. The reciprocal of the Equivalent resistance is equal to the sum of reciprocal
individual resistance.
1 = 1 + 1 + 1
Req R1 R2 R3
PROOF:
Consider three resistances R1, R2 and R3 connected in parallel.
Using Ohm’s law.
V = I R
Apply it to all resistance:
At R1 - V = I1 R1
I1 = V
R1
At R2 : V = I2R2
I2 = V
R2
At R3 : v = I3R3
I3 = V
R3
Replace all three resistance by a single resistance “Req” keeping the potential
difference remains same.
Using Ohm’s law.
V = I R
V = I req
I = v
Req
From the character sticks of parallel combination:
I = I1 + I2 + I3
Substituting the values:
V / Req = V / R1 + V /R2 + V / R3
V / Req = V (I / R1 + I / R2 + i / R3)
This is the required expression.
ALTERNATING CURRENT AND DIRECT CURENT:
ALTERNATING CURRENT:
A current which changes its direction many times in a second is called alternating
current.
Alternating current always flows in the form of cycle which is given as:

DIRECT CURRENT:
A current which does not changes its direction is called direct current.
Direct current always flows in a straight line which is given as”

JOULE’S LAW:
Whenever current passes through any conductor it requires certain amount of energy
to pass through the resistance of the conductor. Battery provides exactly the same
amount of energy. When current cross the resistor it converts such amount of energy
into heat as a result of collision between the vibrating molecules and the free electrons.
“The amount of heat is directly proportional to the work done by the battery for the
flow of current.”
Potential difference is defined as:
Work done per unit charge.
By the definition of potential difference ;
Amount of work required to move IC = W = V.
Amount of work required to move qc = w = Vq.
W = vq ………………….1
But: I = -q
T
q = It ………………..2
Substituting 2 in 1
W = V I T
But: v = I R
W = (I R) It
W = I2 RT
Which is the required mathematical form of Joule’s law and it is expressed as,
“Amount of heat produced is directly proportional to the work required for the flow of
current, the time for which the current is passed and the resistance of the conductor.
POWER DISSIPATION:
“Amount of energy lost in a unit time due to the resistance of the conductor is called
power dissipation.”
OR
“Rate of energy lost is called power dissipation.
MATHEMATICALLY FORM:
P = w
T
But w = I2 RT
p = I2 RT
t

Multiply & divide by “R” P = I2 R x R
R
P = I2 R2
R
P = (IR)2
R
But: V = I R
P = V2
R
ELECTRO MOTIVE FORCE:
DEFINITION:
A force which is required to motivate the electrons to move through the conductor is
called electromotive force. OR
Energy supplied by the battery per unit charge is called electromotive force.
MATHEMATICAL FORM:
EMF = energy supplied
Charge
E = w
q
Unit:
Its unit is volt.
E = w
q
1V = 1J
1C
It shows that:
“If 1J of work is done i.e. 1J of energy is supplied to move 1C charge than it is said that
there is an electromotive force of 1V.”
CAPACITOR:
DEFINITION:
A storing device for the charges is called capacitor.
OR
An electrical device having ability to store the charges at its plates is called capacitor.
CONSTRUCTION:
It consists of two electric plates at a
certain distance from each other.
a battery of potential difference (V)
is connected across the plates to store
the charges (q) at the surface of the plates.
PRINCIPLE / WORKING:
It is based on the principle that:
Amount of charges stored in the capacitor is directly proportional to the potential
difference applied across the plates of the capacitor.
If ‘q’ is the amount of charge stored in the capacitor due to potential difference ‘V’ than
q  V
q = CV
Where,
c = capacitance of the capacitor.
Capacitance is defined as.
“ The tendency of a capacitor to store the charge on its plates.”

FACTORS:
Following are the factors effecting the capacitance of the capacitor.
1. AREA OF THE PLATES:
Capacitance increases with the increase of area of the plates.
2. DISTANCE OF THE PLATES:
Capacitance increases with the decrease of the distance between the plates.
3. NATURE OF THE PLATES:
Capacitance depends on the nature of the dielectric used between the plates
and the use of dielectric increases the capacitance of the capacitor.
UNIT OF CAPACITANCE:
The unit of capacitance is farad.
 q = CV
C = q
V
1f = 1c
1V
It shows that,
“If 1C charge is stored in the capacitor due to 1V battery then the unit is said that there
is capacitance of 1f.”
NUMBERS:
given: q = 2.5 uc
= 2.5 x 10-6C
VA = .60 V
VB = + 10V
To find:
U = ?
Formula:
V = w
q
Solution:
 charge is displacement from A to B
 V = VB - VA
V = 10 – (-60)
V = 10 + 60
V = 70

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NEWTON’S CORPUSCULAR THEORY OF LIGHT:
Newton put forward a theory, called corpuscular theory of light. According to this
theory “a source of light emits out minute particle called corpuscles. When these
particies reach our eye, they produce the sensation of vision.”
Newton’s explained the following phenomenon of light.
i. The rectilinear propagation of light.
ii. The formation of shadow.
iii. The reflection of light.
iv. The refraction of light.
DEFECT:
To explain the refraction, he made wrong assumption that velocity of light in denser
medium is greater than the velocity of light in air.
WAVE THEORY OF LIGHT:
Huygens put forward a theory called wave theory of light. According to this theory”a
Source of light produces the sensation of vision.”
This theory explained the following phenomenon of light.
i. The rectilinear propagation of light.
ii. The formation of shadow.
iii. The reflection of light.
iv. The refraction of light.
DEFECT:
i. To explain the refraction of light, he made the wrong assumption that velocity
of light is smaller in denser medium, than in air.
ii. According to Huygens a source of light produces the wave sensation of vision
since medium is necessary for the propagation of waves, therefore it was
assumed that the entire space was filled with fluid, called ether.
MAXWALL’S ELECTROMAGNETIC WAVE THEORY:
Maxwell’s put forward a theory called Maxwell’s electromagnetic wave theory.
According to this theory, “Since light is considered as electromagnetic waves because
both have same speed and since electromagnetic waves do not need any medium for
their propagation, “ Therefore light waves can travel in space.
DEFECT:
Maxwell’s electromagnetic theory of light failed to explain the process of photoelectric
effect.
EINSTEIN’S PLANK’S QUANTUM THEORY:
QUANTUM THEORY OF LIGHT:
According to Quantum theory of light, “light are composed of bundles or particles of
energy called proton. The energy of each proton is directly proportional to the
frequency of radiation. “
MATHEMATICALLY QUANTUM THEORY OF LIGHT CAN BE EXPRESSED
AS:
Where,
E : Energy of proton
F ; Frequency of the radiations
H ; plank’s constant, 6.63 x 10-34 js.
DISPERSION:
Definition:
“If phenomenon of spreading of White light into its constituent colours is called
dispersion.”
It is explained by a simple experiment show in the fig when a beam of light (sunlight)
entering a dark room through a narrow hole in a wall, falls on a prism, then on coming
out of the prism forms a band of seven colours on the wall. This multicolor pattern of
light is called spectrum. The colors obtained are Violet, Indigo, Blue, Green, Yellow,
Orange and Red (V.I.B.G.Y.O.R)

RAINBOWS:
Sometimes an arc of beautiful colors appears in the sky after a rainfall. It is seen when
sun on the back side of observer. The rain drop behaves like prism and while light
entering the raindrops is splitted into its constituent’s colors. Such phenomenon of
light i.e. the formation of different colors is rainbow.

EMISSION OF LIGHT BY ATOMS:
According to Bohr’s atomic theory every substance consists of atoms. In an atom the
electron revolve round the nucleus in certain allowed orbit. The energy of the electron
in each orbit has definite value. When electron gain in certain amount of energy if
jumps into the higher orbit. Certain amount of energy it jumps into the higher orbit.
The atom is then said to in exited states. The atoms cannot remain with exited for a
long time. When electron jumps back into the lower orbit it emits energy in the form of
photons. The frequency of such light waves (photons) depends upon the orbit in which
electron transit.
THE ELECTROMAGNETIC SPECTRUM:
The spectrums of electromagnetic radiation consist of radio waves, microwaves, visible
waves, ultraviolet waves, x-rays and r-rays. These electromagnetic radiations have
different in their. Wave length frequencies but all they travel with the speed of light i.e.
3 x 10-8 m/s.
I. RADIO WAVE:
These electromagnetic waves have wave length between few millimeters to
several meters.
II. MICRO WAVE:
These electromagnetic waves have wave length between 1 millimeters to 300
meters.
III. INFRARED:
Infra red waves, also called heat waves, have a mean wave length of 10-5 m.
IV. VISIBLE WAVE:
These electromagnetic waves have wave length ranging from 400 millimeters to
700 nm.
V. ULTRA VIOLET WAVES:
There wave length is between 600 nm to 380 nm.
VI. X-RAYS:
The wave length range is from 109 m to 1011 m.
VII. R-RAYS:
There wave length range is from 1011m to 1014 m.
GREEN HOUSE EFFECT AND GREEN HOUSES:
GREEN HOUSE EFFECT:
“Infra red rays are absorbed by carbon dioxide and water vapors present in the
atmosphere and are not radiated back.”
Heat is trapped in this manner and this effect is known as green house effect.
GREEN HOUSE:
A green glass surface which absorbs infrared radiations is called green house.

Reflection of Light and Optical Instruments: Ch 14

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Human Eye:

The eye ball is nearly spherical in structure. Its outer layer is thick and opaque and is called sclerotic. The front portion of sclerotic is called Cornia and it is transparent. Inside the sclerotic there is a black pigment layer called choroids whose font portion known as Iris. At the center of iris, there is opening called pupil of the eye. This iris contracts in bright light and elongate in dim light. In this way the size of pupil is controlled. Behind this iris there is a soft transparent convex lens which forms the image of the object at the back of the eye ball, called retina. There are nerve linings in the retina which are connected to the optic nerves. The sensation of image formed on the retina is conveyed to the brain through optic nerve.

The lens is supported by ciliary muscles which can increase or decrease the curvature of the lens thus changing the focal length of lens. The focal length of lens changes to the distance between the object and the eye so that clear image is formed at the retina.

Defects of vision:

1. SHORT SIGHTEDNESS (MYOPIA)

The eye having this defect can see near objects clearly. The distant objects are not clearly visible. This defect may be due to eye ball of large size or short focal length of the eye lens. In this defect the image of the distant object is formed in front of retina. This defect may be corrected by using a concave lens.

2. LONG SIGHTEDNESS (HYPERMETROPIA)

The eye having this defect can see distant objects clearly. The near object are not clearly visible. This defect may be due to eyeball of small size or long focal length of the eye lens. In this defect the image of the near object is formed behind the retina. This defect may be corrected by a using convex lens.

ASTIGMATISM:

If the cornea of the surface of the eye is not perfectly spherical. The eye has different focal point in different planes and the image is not clearly formed on retina. Astigmatism is connected by using a symmetrical lens having different radii of curvature in different planes.

LACK OF ACCOMMODATION (PRESBYOPIA):

At old age the ciliary muscles get weak resulting in the lack of accommodation. This defect is called presbyopia and can be corrected by using bi-focal lenses. The convex part is on the lower side to see near objects and concave part in the upper Side to see the distant object clearly.

CAMERA:

It is an optical instrument by which permanent image of an object is obtained on a sensitive screen. It consists of a light proof container blackened inside to absorb energy (light). In ordinary camera, a convex lens is situated at the front to produce real and inverted image of the object on the screen situated at the back of the camera. The lens of the camera can be moved in or out with the help of mechanical mount in order to

get sharp image.

There is a shutter between the film and the lens. When a photograph is taken, the shutter opens for a while and close by pressing a button. Thus light is made to fall for a very short time on the sensitive screen.

The formation of clear images depends on following factors:

i. Diameter of the aperture of the camera.

ii. Focal length of the lens.

Total internal reflection:

When a ray of light enters from denser to rarer medium it bends away from the normal, therefore the angle of refraction r is greater than the angle of incidence.

When angle of incidence increases, the angle of refraction also increases but it remains greater than the angle of refraction. At certain angle of incidence, angle of refraction becomes 90o . This angle of incidence is called critical angle. If angle of incidence is made greater than critical angle the angle of refraction becomes greater than 90o and the light is totally reflected back into the same denser medium. (As shown in fig). This

phenomenon is called total internal reflection.

Porpagation and Reflection of Light: Chapter 13, Academy of Physics Karachi

Physics tutors.

Q1. Define reflection of light. State the laws of reflection.
Ans: REFLECTION OF LIGHT:
When light is incident from one
medium to another medium then
whole or some part of light
bounces back into the first this
phenomenon is known as reflection
of light.
The amount of light reflected depends
upon the nature of light and the nature of
reflecting medium. Light is well reflected
from a smooth and glossy surface.
LAWS OF REFLECTION:
There are two laws of reflection:
1. The angle of incidence is mathematically, we can write.
Angle of incidence = Angle of reflection
 i =  r
2. This incident ray, the reflected ray and the normal all lie in the same plane.
Q2. What is meant by regular and irregular reflection of light? Describe importance
of irregular reflection in daily life. Or
Differentiate between regular and irregular reflection.
Ans:
REGULAR REFLECTION IRREGULAR REFLECTION
1. Reflection of light from smooth,
Polished surface is called regular
reflection.
2 If parallel rays of light fall on regular
surface all rays are reflected in the
same direction and same angle. Reflection of light from a rough surface is
Called irregular reflection.

When parallel rays of light fall on irregular
surface angle of incidence is not equal to the
angle of reflection.

IMPORTANCE OF IRREGULAR REFLECTION:
Irregular reflection plays an important role in nature. It is due to this reflection that we
can able to see the non-luminous objects when light strikes on them. Also dust and
other panicles hanging in the atmosphere scatter sunlight in all directions and as such
we get sufficient light in our rooms and other places where sunlight cannot reach
directly. Its due to this fact that sunlight reaches us before sunrise and persists for some
time even after the sunset.
Q3. Explain the formation of a image by a plane mirror.
Ans: IMAGE FORMED BY A PLANE MIRROR:
Consider an object ‘O’, placed in front of a plane mirror. The rays of object ‘O’ are
reflected by the plane mirror M and enters our eye. The line which joins the image I
and the object O makes an angle of 90o with the surface of the mirror M. From the
geometrical construction, the distance OM and IM are equal. Therefore, we feel that
the light rays from I, but in fact they come from ‘O’ and reflected by the mirror. At the
mirror surface we find that the angle of incidence is equal to the angle of reflection.

Observing the images formed by a plane mirror we note four main characteristics of
the images which are following:
1. Images are found to be laterally inverted, that is the right side of the object
appears as the left side of the image.
2. Images are found to be of the same size as that of the object.
3. The image formed is found to be virtual, that is, it cannot be obtained on a
screen.
4. The image is as far behind the mirror as the object, is in front of the mirror.
Q4. What are spherical mirrors? Also define the following terms:
(a) Center of Curvature (b) Radius of Curvature (c) Pole of Mirror
(d) Principal Axis (e) Principal Focus (f) Focal Length
Ans: SPHERICAL MIRRORS:
A spherical mirror is a portion of the surface of a polished hollow, sphere.
The spherical mirrors are of two types.
CONVEX MIRROR OR DIVERGING MIRROR:
The spherical mirror whose outer surface (convex shape) is made reflecting is known as
convex mirror.
CONCAVE MIRROR OR CONVERGING MIRROR:
The spherical mirror whose inner surface (concave shape) is made reflecting is known
as Concave mirror.

(a) CENTER OF CURVATURE:
The centre of that hollow glass sphere, whose part is the spherical mirror is known as
center of curvature of mirror denoted by “C”.
(b) RADIUS OF CURVATURE:
The radius of that hollow glass sphere whose part is the spherical mirror is known as
radius of curvature of the mirror on diagram CM is the radius of sphere.
(c) POLE OF MIRROR:
The central point of the spherical mirror is known as pole of mirror.
(d) PRINCIPAL AXIS:
The straight line passing through the center of curvature and pole of the mirror is
known as principal axis of spherical mirror.
(e) PRINCIPAL FOCUS:
When a beam of light parallel to the principal axis and reflect to the concave mirror it
converges to a point on the principal axis. In the case of convex mirror when a beam of
rays parallel to the principal axis and reflect to the convex mirror it appears to diverge
from a point on the principal axis. This point is called the principal focus “F”.
(f) FOCAL LENGTH:
The distance between principal focus F to P is called focal length. It is denoted by f.
Q5. Differentiate between real and virtual images?
Ans:
REAL IMAGE VIRTUAL IMAGE
1.An image is said to be real if the rays of
light actually pass through a point or
converge a point. A virtual image is only visible to eye and the
reflected rays of light to come from one point
or diverge one point.
2.The real image can be seen on screen Virtual image cannot be seen on a screen.
3. The distance of real images and
objects are taken as positive Distances of virtual objects and images are
take as negatives.
Q6. An object is moved from infinite distance towards pole concave mirror then
illustrate the nature of image formed at different positions.
OR
Write the image location in a concave mirror with the diagram when the object is
at:
i. Infinity
ii. Beyond ‘C’
iii. At ‘C’
iv. Between ‘F’ and ‘C’
v. At ‘F’
vi. Between ‘F’ and ‘P’ or with in focal length.
Ans: 1) OBJECT IS AT INFINITY
POSITION:
When an object is at infinity to the mirror
then image is formed at principal focus ‘F’
NATURE:
It is real and inverted,
Size:
Image is extremely diminished.
2) OBJECT BEYOND ‘C’
POSITION:
When an object is placed beyond ‘C’ then
image is formed between ‘F’ and ‘C’.
NATURE:
It is real and inverted.
SIZE:
Image is diminished.
3) OBJECT IS AT ‘C’
POSITION:
When an object is at ‘C’ then image is
formed at center of curvature.
NATURE:
It is real and inverted.
SIZE:
Image is equal in size.
4) OBJECT LIES BETWEEN ‘F’ AND ‘C’
POSITION:
When an object lies between ‘F’ and ‘C’
then image is formed beyond ‘C’.
NATURE:
It is real and inverted
SIZE:
Image is magnified.
5) OBJECT IS AT ‘F’
POSITION:
When an object is placed at principal focus
then its image is formed at infinity.
NATURE:
It is real and inverted.
SIZE:
Image is extremely magnified.
6) OBJECT IS PLACED BETWEEN ‘F’ AND ‘C’
POSITION:
When an object is placed between ‘F’ and ‘P’
then image is formed behind the mirror.
NATURE:
It is virtual and erected.
SIZE:
Image is magnified.
Q7. Derive mirror equation using concave mirror.
Ans: MIRROR FORMULA (EQUATION FOR SPHERICAL MIRROR)
Suppose an object “AB” is placed between
‘F’ and ‘C’ of the concave mirror.
Two rays AP and AD are incident on the mirror.
Ray AP is reflected with the same angle along
the direction PA’ obeying the law of reflection.
As A ‘ PB ‘ and APB are similar.
Therefore, AB / PB = A ‘ B ‘ / PB ‘
AB / A ‘ B ‘ = P B / PP
Or ho / hi = p / q

Ray AD which passes through ‘F’ becomes parallel to the principal axis PB.
As  ABF =  FPD
AB / BF ‘ = DP / F’ P
AB / DP = BF ‘ / F ‘P
As AB = ho, DP = A ‘ B ‘ and A ‘ B ‘ = hi , F ‘ P = f and BF ‘ = p – f
But as ho / hi = p ‘ - q / f ………..(2)
From equation (1)
ho / hi = p / q
p / q = p- f / f

dividing both sides by ‘p’
p / pq = (p – f) / fp
p / pq = (p / pf) - (f / fp )
I /q = I /f - I / p
I / f - I / p = I / q
This equation is known as mirror equation:
Q8. How a concave mirror is used on head lights and search lights to throw light at a
Long distance.
Ans: In head lights and in search lights the electric lamp is placed at the focal point of
concave mirror. So that light rays become parallel after reflection from concave mirror.
so that these do not scatter and reach at large distance.
Q9. Give some uses of spherical mirrors?
Ans: There are some important uses of spherical mirrors.
i. A concave mirror is used in micro scope to illuminates the object.
ii. They are used in objectives of telescopes.
iii. These mirrors are used by the doctors to examine eyes, throat, and noses of
patients.
iv. The spherical mirrors are uses in head lights of automobiles.
v. These are also used in shaving mirrors.
Q10. Describe structure and working formula.
Ans: STRUCTURE:
It consists of a rectangular box, a very small hole on one side and frosted glass plate,
tracing paper or photographic film on the opposite side.
WORKING:
A narrow pencil of rays staring from point A passes through the pinhole ‘O” and
illuminates a small area at ‘A’. Similarly a narrow pencil of rays starting from ‘C’
illuminates a small area at ‘C’. In this way points lying between A and C illuminate
corresponding points between ‘A’ and ‘C’ and a real and inverted image A’C’ of the
object AC is formed on the back of the camera.

Waves and Sound: Chapter 12, X Physics,03362023305, Online Physics Academy Karachi

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Q1. Define Simple Harmonic Motion.
Ans: The vibratory motion of a mass attached to a spring is called simple harmonic motion.
The motion in which acceleration is always proportional to its displacement and the
acceleration is always directed towards the equilibrium position is called simple
harmonic motion.
Q2. Derive the expression of Simple Harmonic Motion.
Ans: SIMPLE HARMONIC MOTION:
Consider a block al rest in its equilibrium position on a frictionless the block to right,
there will be a restoring force “F” exerted on the block by the spring and this force is
directed to the left according to Hook’s.
F  - X
F = Kx
Since direction of displacement is opposite to that
of restoring force. According to Newton’s second law.
F = ma = - Kx
a = -x
This is basic equation of motion for an object undergoing simple harmonic motion.
Since,
K = constant and mass = constant
a = (constant) X
a = KX
M
a = - (displacement)
Q3. Define simple Harmonic Motion with the help of:
(a) pendulum (b) mass suspended by a spring
Ans: (a) PENDULUM:
Motion of pendulum is simple harmonic
motion because when pendulum is moved
from its mean position a restoring force
is set which is always opposite to the
direction in which it is displaced.
(b) MASS SUSPENDED BY A SPRING:
When mass is suspended by a spring, and it is moved downwards a restoring force is
set which is always opposite to the direction in which it is displaced.
Q4. Define the following terms:
i. Vibration ii. Time iii. Period iv. Frequency
v. Displacement
Ans: i. Vibration:
A vibration means one complete round trip of a body e.g. incase of simple pendulum
if it is displaced to its max value it will move to other extreme value and returns back to
the initial point this is one vibration.
(ii) TIME PERIOD:
It is the time required to complete one vibration or oscillation. It is measured in seconds.

(iii) FREQUENCY
It is the no. of vibrations in one second. It is expressed as vibration /sec, cycles/sec or
hertz. It is denoted by the reciprocal of time period.
(IV) DISPLACEMENT:
Displacement of a vibrating body at any instant is, its distance from the equilibrium
position at that instant.
(V) AMPLITUDE:
It is the maximum displacement of a body on either side of its equilibrium position.
Q5. Prove that motion of a simple pendulum is an example of Simple Harmonic
Motion.
Ans: Simple Pendulum:
An ideal simple pendulum consists of a point mass
Suspended by weights and inextensible string from
A fixed support. If we displace the bob from its mean
Position ‘O’ to a new point “A”, it will move forwards
“O” * under the motion of gravity. The bob will may
come to rest as “O” but due to inertia it will continue
to move towards a point “B”. While moving from point “O” to “B” bob moves against
the gravity so its velocity continues to decrease at “B”. It becomes zero now bob once
again moves from “B” to “O” under the action of gravity and from “O” to “A”. This
process is repeated again and again. As the bob is at its lowest point. Its potential
energy is zero but kinetic energy is maximum whereas at the two extreme values
kinetic energy becomes zero and potential energy known as transverse wave, waves
produced in the string is an example of transverse wave.
LONGITUDINAL WAVE:
If the motion of the particles of the elastic medium is back and forth along the
direction of propagation of the wave then this tube of wave is, known as longitudinal
wave. Examples are the waves produced by waving the spring back and forth and
sound wave in air is one of the examples of longitudinal.
Q6. What is Ripple Tank?
Ans: Take some water in a large tray take a meter rod to which a handle is attached. Dip the
meter rod in water and move it up and down. As the meter rod vibrates waves once
produced in the form of crest and trough. Place a small cork on the on the water as the
waves pass over the cork, it will vibrate up and down perpendicular to the direction of
the waves at its own place. This shows that as the wave travel along the water surface,
water particles vibrate perpendicular to the direction of waves, but they do not leave
their position.
Q7. What is the relation between, velocity, wave length and frequency?
Ans: Consider a wave of wave length “  “ and frequency “ v “ traveling with velocity “V “ in
required for the wave to travel a distance of one wave length “  “ so that.
 = VT
The frequency of the wave is naturally determined by the frequency of vibrating
particle. v = I / T OR
T = I / v
Substituting the value of “T” in equation.
 = VT X
 = V / v
v = V / 
V = v 
Q8. Define “Crest” and “Trough”.
Ans: CREST
The projections of the waves are called crest.
TROUGH:
The depressions of the waves are called trough.
Q9. Define wave length.
Ans: WAVE LENGTH:
The distance below two consecutive crest and trough is called wave length. It is
denoted by “  “ read as lambda.
Q10. What is sound wave?
Ans: SOUND WAVE:
The longitudinal waves that are due to a vibrating source and that are capable of
producing a sensation in the auditory system are called “sound waves “.
Q11. What is mean by Resonance? Give its examples.
Ans: When the frequency of the driving force “V “ is exactly equal to the natural frequency of
the oscillator “n “ the driving force imparts the maximum energy to the oscillator
resulting in considerable increase in amplitude of vibration a condition called
“Resonance”.
Resonance occurs when ever a system is set-in oscillation at its own natural frequency
as a result of impulses received from some other system which is vibrating with the
same frequency.
Example:
While crossing the bridge, the soldiers are ordered not to march in steps but to break
their steps. The reason is that the bridge receives periodic impulses by regular foot
steps of a marching column of soldier if the time period of periodic impulses happens
to by equal to the natural time period of the bridge, a vibration of dangerously large
amplitude may be produced and bridge may collapse.
Q12. What are the characteristics of sound?
Ans: Following are the characteristics of sound.
a) INTENSITY AND LOUDNESS:
It is the average power crossing a unit area of surface perpendicular to the
direction in which the sound waves are traveling.
In M.K.S.System unit of intensity I s watt per wave is proportional to the square
of the amplitude of sound wave.
Loudness is closely related to intensity the loudness “ L “ and intensity level are
related by L = I l 03
16 L
b) PITCH:
The frequency of pure sound is a physical quantity this frequency produces a
stimulus to the ear. The sensation corresponding to this is called “Pitch” of
sound. Pitch of sound depends upon frequency of the vibrating body. Pitch is
measured in Hertz.
c) QUALITY:
Ear possesses great sensitivity to quality of sound. It is the quality which makes
possible for us to distinguish among the voices of our friend even when they
have been distorted by telephone transmission.
Q13. Derive the expression of wave velocity.
Ans: The speed of a wave is the distance traveled by it in unit time (in the direction of wave).
Velocity = Distance = Wavelength
Time Time Period

V = T
But T = I
F
Hence V = f 
Q14. What are the two important properties of waves?
Ans: Bouncing back of wave from a surface is called reflection. The angle at which the
wave is reflected is equal to the angle at which the wave is incident on the surface.
Waves coming from the source and hitting on obstacle in berries called reflected
waves have the same frequency because they are produced by the same source.
INTERFERENCE:
Interference means the interaction of two waves passing through the same require
of space at the same time.
When two sets of waves meet, they are neither reflected nor absorbed by each other
one simply passes all the other.
How was at that point where the algebraic sum of the displacements of the two
separate waves.
CONSTRUCTIVE INTERFERENCE:
If at a given point the crests or trough of the
two waves a simultaneously then the combined
waves is large than either of the two waves. This is
called constructive interference.
DESTRUCTIVE INTERFERENCE:
If the crust of one wave arrives simultaneously with the
trough of the other wave then the two will cancel each other and no wave will be of
observed. This is called destructive interference,
Q15. Define Stationary Waves.
Ans: If two waves of the same amplitude and frequency traveling in opposite direction
meet one another the resulting interference pattern gives rise to what are called
standing waves or stationary waves.
Q16. How is sound produced?
Ans: SOUND IS PRODUCED:
Sound is a form of energy which is produced by a vibrating body.
PROPAGATION OF SOUND WAVES:
When a body was is vibrating it produces a disturbance in the surround air. This
distance reaches our ear in the form of waves this producing the sensation of sound.
Experiment:
Suspended an electric bell in a jar by its waves through a cork fined in its mouth. Switch
on the bell. We will hear the sound of the bell. Now start remaining air from the jar
with the help of an exhaust pump. The loudness of the wound of the bell will start
decreasing. This experiment shows that the air is necessary for the propagation of
sound.
Q17. What is an audible frequency range?
Ans: Our ear can hear only those sounds whose frequency is between 20 Hz to 20,000 Hz.
That is, the ear can neither hear a sound of frequency less tan 20 Hz nor a sound of
frequency greater than 2.0,000 Hz. A sound or frequency greater than 20,000 Hz can
be produced but the human ear cannot detect it because ear drum cannot vibrate, with
such a high frequency. The second having a frequency more than 20,000 is known as
ultrasonic. The audible range (20 Hz to 20,000 Hz) is different, for different persons and
it also varies with the age.
Q18. How is echo produced?
Ans: The sound heard after reflection from a surface is called an Echo. In a normal human
ear the effect in the sensation of sound period for 1/10th of a second after the sound
has ceased. If some sound enter the ear with in this interval of time it merges with the
previous sound and does not appear to be separate . It hear an echo it is therefore
necessary that the time elapsed between the production of a sound and the hearing of
is echo is equal to or more than i/10th of a second.
Q19. Explain Beats.
Ans: Beats can be defined as the periodic variation in intensive at a given point due to the
superimposition of two waves having slightly different frequencies. The number of
beats one hears per second, or the best frequency is equal to the difference in
frequency between the two sounds. The minimum beat frequency that a human ear
can detect is beats per second.
EXAMPLE:
If two tuning forks of slightly different
frequencies are struck we hear a sound
of alternating high and low intensity this
is called a beat and hence the
phenomenon is popularly called beats.
Q20. Define Ultrasonic Waves.
Ans: DEFINITION:
i. Ultrasonic waves are longitudinal waves with frequency above the audible
range. Ultrasonic waves are widely used as diagnostic, therapeutic, and
surgical tools in medicine and in industrial application.
ii. Ultrasonic waves can be used echo-depth sounding devices to determine the
depth of the sea.
iii. Sonar (sound navigation and ranging) is used because it units Ultrasound wavesand can be used to carry out the location of an object by its echo.
iv. Ultrasound are often preferred to x-ray scans, because Ultrasound is much refer
than x-rays.

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Monday, May 31, 2010