Nuclear Physics

Nuclear Physics
It is the branch of Physics that deals with the structure, properties and reaction of particles found in the nuclei of atoms.
Radioactivity
The phenomenon of emission of radiation from Uranium and other substances is known as radioactivity. The substances that emit radiation are known as radioactive elements.
Experiment
A small quantity of a radioactive element such as radium is placed in a cavity of a lead block in such a way that the radiation from radium can only come out through this cavity. A photographic plate is placed at some distance above the lead block so that the radiation from radium falls upon it. The apparatus is placed in a vacuum light chamber which is evacuated by a powerful pump. This chamber is then placed between the poles of a powerful magnetic field. Under the action of magnetic field, two or three types of radiation are deflected forming three separate images on the photographic plate.
Properties of Alpha Particles

• Alpha particles are Helium nuclei.
• The charge on alpha particles is positive.
• The velocity of alpha particles is 1/100th of the velocity of light.
• Ionization power is greates.
• Penetration power is the least.
• It effects the photographic plate.
• It produces florescence with zinc sulphide solution.

Properties of Beta Particles

• Beta particles are fast moving electrons.
• The charge on beta particles is negative.
• Its velocity is slightly less than the velocity of light.
• Ionization power is less than alpha particles.
• Its penetration power is greater than alpha particles.
• It effects the photographic plate.
• It produces florescence with barium platino cyanide solution.

Properties of Gamma Rays

• Gamma rays are electromagnetic in nature.
• They are neutral rays.
• Its velocity is equal to the velocity of light.
• Ionization power is least.
• Its penetration power is the greatest.
• It effects the photographic plate.
• It produces florescence with Barium Platino Cyanide.

Nuclear Fission
The splitting of a nucleus into fragments with the emission of energy when bombarded by a neutron is called a fission process.
Chain Reaction
In a fission reaction, each nucleus emits three neutrons. These neutrons collide with other uranium nuclei and cause fission in them emitting three more neutrons. These neutrons produce further fission in other nuclei and this process continues. This is called a Chain Reaction.
Nuclear Reactor
A system used to obtain a controlled amount of heat from nuclear fission is called a nuclear reactor.
Working of a Nuclear Reactor
The fission material in a nuclear reactor is Uranium. This is called fuel element. The neutrons released from fission move with high velocities. The fast moving neutrons have to be slowed down before they cause further fission. The process of slowing down neutrons is called moderation. heavy water is used as a moderator. When a chain reaction starts, it may produce large number of neutrons, which may cause too much fission. The rate of chain reaction is controlled by inserting control rods which are commonly made of Boron.
The heat produced is a nuclear reactor is carried away by the circulation of pressurized water or carbon dioxide gas inside the core of the reactor. This heat is used to produce steam. This steam can be used to run a power station for the generation of electricity.
Nuclear Fusion
The process in which two lighter nuclei are brought together to form another heavy nucleus is called the Fusion Reaction.
When Deuterium and Tritium nuclei are brought together they form a Helium nucleus and release a large amount of energy and a neutron

Electronics

Definitions 1. Electronics
Electronics is a branch of Physics, which deals with the development of electron emitting devices, their utilization and controlling electron flow in electrical circuits designed for various purposes.

2. Semi Conductor
Substances whose electrical resistance lies between those of conductors and insulators are known as semi-conductors.

3. Doping
Mixing of any tetravalent element into a trivalent or pentavalent element so that its electrical conductivity increases is called dopping.

4. n-Type Substance
A pure semiconductor with a valency of three, doped with a pentavalent element is called n-type semiconductor.

5. p-Type Substance
A pure semiconductor with a valency of three doped with a trivalent element is called n-type semiconductor.

6. Diode
The common boundary of n-type and p-type regions in a semiconductor is called p-n junction diode. It allows the current to flow in only one direction.

7. Forward Biased
If the p-type material of a semi conductor diode is at a positive potential and the n-type material is at a negative potential then the diode is forward biased. It has a very low electrical resistance.

8. Reverse Biased
If the p-type material of a semi-conductor diode is at a negative potential and the n-type material is at a positive potential then the diode is reverse biased. It has a very high electrical resistance.

9. Rectification
The process of conversion of alternating current into direct current is known as rectification.

10. Rectifier
A rectifier is a device that converts Alternating current into Direct current.

11. Transistor
A transistor is a semiconductor, which consists of a thin central layer of one type of semiconductor material sandwiched between two relatively thick pieces of the other type of semiconductor. The central part is known as the base (b) and the pieces at either side are called the emitter (e) and the collector (c).

12. npn Transistor
The npn transistor has a thin piece of p-type substance sandwiched between two pieces of n-type semiconductors.

13. pnp Transistor
The pnp transistor has a thin piece of n-type substance sandwiched between two pieces of p-type semiconductors.
Telegraph
Introduction
A telegraph is a device that is used to send and receive messages between two distant points.
Construction
An electric telegraph consists of a battery that is connected to a buzzer through the tapping key. There is only one wire between the buzzer and the tapping key. The circuit is completed by connecting the other terminal to the ground few feet below. The earth being moist acts as a good conductor.
Working
When the tapping key is pressed, the receiver produces a buzzing sound. The interval between two buzzing sounds can be controlled by the interval between pressing the tapping key. The international Morse Code, which is a combination of dots and dashes is used to send and receive messages with the help of telegraph.
Radio
Introduction
A radio is a device for receiving and sending speech or music over large areas by electromagnetic signals.
Working

1. Transmission: Information is sent out into the atmosphere from a transmitting station. When someone speaks in the microphone at the radio station, sound waves are converted into electrical fluctuating current. This current is converted into high frequency alternating current, which is allowed to pass in the transmitting antenna. The transmitting antenna produces radio waves with fluctuating amplitude. These waves are known as modulated carrier waves.
2. Receiving: When the modulated carrier waves meet a receiving aerial, they generate fluctuating alternating current in it. This AC is converted into DC with the help of a rectifier. An earphone or a speaker is connected to the receiver. The DC energizes the electromagnet of the speaker and causes the diaphragm to vibrate. This produces the sound of same frequency as that at the radio station.
Radar
Introduction
Radar stands for Radio Detection and Ranging. It is used to detect and find out the distance of distant object with the help of radio waves.
Construction
It consists of a transmitter, a receiver and several indicating devices.
Working
1. Transmission: The transmitter generates very high frequency electromagnetic waves in the desired direction with the help of a concave antenna.
2. Receiving: These rays after striking an object are reflected back and are received by the radar antenna. The antenna feeds these rays in the indicating devices.
3. Processing: The indicating devices measure the time taken by the waves to return. They calculate the wave velocity and finally the distance of the object.
Radar waves can penetrate fog, clouds, haze and smoke.
Telephone
Introduction
A telephone is a device by which two persons at distant places can directly talk to each other through electric current carrying wires.
Construction
A telephone system consists of a microphone and a receiver.
1. Microphone: The microphone consists of a diaphragm suspended in front of packing of carbon granules.
2. Receiver: The receiver has an electromagnet and a diaphragm made of magnetic alloy in front of it.
Working

1. Transmission: When someone speaks in front of the microphone, the diaphragm vibrates due to the sound waves. The compressions and rarefactions of the sound waves cause the diaphragm to increase and decrease the pressure on carbon granules. This results in the increment and decrement in the resistance offered by the granules and hence generates fluctuating current.
2. Receiving: At the receiver, the electromagnet receives fluctuating current, which generates a fluctuating magnetic field. The diaphragm in front of the electromagnet also vibrates with different amplitudes and generates sound of same frequency as spoken at the other end.
TV Camera
Working
For the purpose of TV Transmission, TV Camera focuses on object to be televised. The convex lens of the TV Camera produces an image on the thin sensitive plate known as mosaic screen. The mosaic screen is fixed in the camera and has the ability to emit electrons. When light is stronger, more electrons are given out the material making positive at this location. The beam of electrons from the electron gun in the camera tube is meant for scanning the back surface of the mosaic screen along the successive longitudinal lines in it. Special magnetic deflection system achieves this purpose. As soon as the beam hits on an area with high positive charge, few of the negative charges are repelled. If the positive charge is less, more of the electrons are emitted. After the collection of these electrons it is converted into voltage pulse known as video signal. The video signals that have been amplified are utilized to manufacture very high frequency. This frequency is received by a television antenna, which reverses the process and gives us a clear animated picture on the screen

Magnetism and Electromagnetism

Magnet Metals like iron, nickel and steel attract each other magnetically. They are called magnets and always point in a particular direction when suspended freely in the air.
Non-Magnetic Substances
Substances that are neither attracted nor repelled by a magnet are called non-magnetic substances. Examples are wood, glass and paper.
Ferromagnetic Substances
A substance which behaves like a magnet in the presence of a strong magnetic field is called a ferromagnetic substance..
1. Hard Ferromagnetic Substances
The ferromagnetic substances which retain their magnetism when removed from the magnetic field are known as hard ferromagnetic substances. Example is steel.
2. Soft Ferromagnetic Substance
The ferromagnetic substances which become magnets in the presence of a magnetic field and lose their magnetism when removed from the magnetic field are known as soft ferromagnetic substance. Example is soft iron.
Magnetic Field
The space surrounding a magnet in which its magnetic effect is felt is called a magnetic field. It is the region within which the magnet can exert its magnetic force.
Methods of Making Magnets
1. Single-Touch Method
Take a hard steel bra and rub it with one end of a magnet in the direction from S to N, keeping the magnet in an inclined position. On reaching the end N of the steel bar, bring the same end of the magnet to the end S of the steel bra and rub it again. Repeat the process several times and the steel bar will be magnetized. The end S will have the same polarity as that of the rubbing pole of the magnet and the end N will have the polarity opposite to that of the rubbing pole.
2. Electrical Method
Take a U-shape steel bar and wound it with an insulated copper wire making sure that the two core arms are wound in the opposite directions. Connect the coil to a battery and pass strong current. The steel bar becomes a magnet as long as current passes through them. In a similar way, a bar can be magnetized by putting it inside a solenoid and passing current through the solenoid. The polarity of the magnet is determined by the direction of the current.
Demagnetization
There are three methods for demagnetizing magnets.
1.Hammering
Magnets can be partially demagnetized by hammering them when they are pointing in the east or west direction.
2. Heating
Magnets loose their magnetism when they are heated strongly.
3. Electrical Method
The most efficient method of demagnetizing a magnet is to use n alternating current. Take a solenoid and place it in the east west direction. Pass an alternating current (about 12 V) through it. Now, put the magnet in the solenoid from one end and pull it out from the other. While the current is still flowing. The magnet will loose its magnetism.
Alternating current reverses its direction at a rate of 100 times per second and hence causes the magnetism of the material to reverse the polarity at the same rate. Due to this rapid reverse in the polarity, the magnet looses its magnetism.
Magnetic Effect of Current
When an electric current passes through a straight wire a magnetic field is created which consists of field lines in concentric in concentric circles with the wire at their center.
Right Hand Rule
The direction of the magnetic field can be determined by the following rule:
“Imagine the wire to be grasped in the right hand with the thumb pointing along the wire. The direction of the fingers will give me direction of the magnetic lines of force.”
Solenoid
A coil of insulated copper wire in the form of a long cylinder is called a solenoid.
Magnetic Field of a Solenoid
When an electric current is passed through a solenoid a magnetic field is produced which is very similar to that of a bar magnet. One end of the solenoid acts as the north pole and the other as the south pole. The magnetic field inside a solenoid is very strong because the lines of force are parallel and close to one another. The magnetic field outside the solenoid is very weak.
Electromagnet
If soft iron is inserted in the core of a solenoid, the magnetic field due to the current in the solenoid is multiplied by thousands. When the current is switched off, the magnetic field disappears. Such a magnet which can be energized by an electric current is called an electromagnet.
Applications of Electromagnets
Industry
They are used to transport heavy pieces of iron and steel safely from one place to another. With the help of electromagnets, iron from mixture is separated.
They are used to produce strong magnetic fields for high power motors and generators.
1. Electric Bell
Construction
An electric bell consists of an electromagnet. One end of the winding is connected to a terminal (T1). The other end is connected to a spring, which is mounted on a soft iron strip called “Armature.” A rod is attached to the armature with its free end having a small hammer that can strike against the bell. a very light spring is attached to a contract adjusting screw which is joined to the second terminal (T2) by a wire. The electric circuit is completed by connecting the terminals to a batter and a switch.
(Diagram)
Working
When the push button switch is pressed, the circuit gets closed and the armature is attracted towards the electromagnet. The spring also gets detatched from the screw. This results in opening the circuit and the electromagnet gets demagnetized. The attraction disappears bringing back the spring to its original position. As soon as the spring touches the screw, the circuit gets closed and the magnet starts to work. It again attracts the armature and this process is repeated as long as the switch is turned on. As a result, the armature vibrates and hammer attached to it strikes the gong. Hence, the bell rings.
2. Telephone Receiver
Introduction
A telephone receiver is a device that converts electrical energy into sound energy.
Construction
The ear piece consists of a permanent magnet in contrast with two electromagnets. A diaphragm of magnetic alloy is positioned in front of the electromagnets.
Working
When the message is transmitted from the other apparatus, sound energy is converted into electric current and is transported to the ear piece through the line. This electric current varies in magnitude depending upon the frequency of the sound waves. In the telephone receiver, the current passes through the electromagnet and energizes the magnet. In this way, the magnetic field strength varies as the current changes. The magnetic force that pulls the diaphragm also varies accordingly. The diaphragm therefore vibrates and gives rise to sound of the same frequency as spoken at the other end.
Fleming’s Left Hand Rule
“Place the fore finger and the second finger of the left hand at right angles. Then, if the fore finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of the motion.”
Galvanometer
Introduction
A galvanometer is a sensitive and delicate device used to measure the magnitude and direction of small currents.
Principle of Galvanometer
The principle of Galvanometer is based on the interaction of the magnetic field produced by a current forcing in a conductor and the magnetic field of permanent magnet. In this instrument, electrical energy is converted into mechanical energy.
Construction
A rectangular coil of wire is wound on a light frame with a pointer attached on the top. The coil frame is pivoted between the jaws of a large horseshoe magnet. At both ends of the coil, hairsprings are attached. These springs help in keeping the coil at zero potential and also provide the path for entry and exit to the current. A soft iron cylinder is fixed in the core of the coil to enhance the force of conductor. The concave shape of the poles of the horseshoe magnet combined with the cylindrical shape of the core creates the radial field to ensure that the field lines are always perpendicular to the coil.
Working
When current passes through the coil a couple of opposite forces are produced and causes the coil to rotate. By the motion of the coil, pointer moves on the scale and galvanometer is used to determine the magnitude and direction of current.
Ammeter
Introduction
A galvanometer having a low resistance in parallel is called as ammeter. It is used to measure current. The low resistance connected in parallel is called shunt.
Working
When current is passed through a Galvanometer, its coil is deflected and pointer attached with the coil moves over a scale. The range for the measurement of current in a galvanometer is very small. Therefore, a low resistance in parallel is used with a galvanometer. This resistance by passes a great part of the current. Only a small amount of current passes through the galvanometer coil, which is within the range of the galvanometer. This resistance acts as a shunt. An ammeter is always placed in series with other circuit components through which current is to be measured.
Voltmeter
Introduction
A galvanometer having high resistance in series is called a voltmeter. It is used to measure potential difference.
Working
The potential difference across a resistance is directly proportional to the current passing through it. As the deflection of the pointer is directly proportional to the current, therefore the deflection of the pointer is directly proportional to the potential difference. A small potential difference produces a full-scale deflection in a galvanometer. In order to measure high potential difference, a high resistance is connected in series with the galvanometer. Most of the potential difference drops across the high resistance. The value of resistor connected in series depends upon the range of the voltmeter. In order to measure the potential difference, a voltmeter is always connected in parallel to the circuit components

Electricity

Definitions 1. Insulators
Those material objects that do not allow charge to pass through them are known as Insulators or non-conductors.

2. Conductors
Those material objects that allow the charge to pass through them are called conductors.

3. Semi Conductors
Those material objects that allow some charge to pass through them are called Semi-Conductors.

4. Free Electron
Those electrons that are loosely bound by their atom and can move freely within the material are called free electrons.

5. Dielectric
The medium or space (vacuum) between two charges is said to be dielectric.

6. Force of Attraction
When two charges attract each other the force is called force of attraction. It has a negative sign.

7. Force of Repulsion
When two charges repel each other the force is called force of repulsion. It has a positive sign.

8. Equivalent Resistance
The relative resistance that has equal value to the combined value of a resistor of a circuit is called equivalent resistance. It is denoted by R(E).

9. Direct Current
Such a current that does not change its direction is known as direct current. It is denoted by DC, which is obtained from primary and secondary cells.

10. Alternating Current
Such a current that reverses its direction with a constant frequency from positive to negative and negative to positive direction is known as Alternating Current, obtained by generators. It is denoted by AC.

11. Conventional Current
An electric current considered to flow from points at positive terminal potential to points at negative potential.

12. Primary Cell
A voltaic cell in which the chemical reaction that produces the e.m.f is not reversible is known as Primary Cell.

13. Secondary Cell
An electric cell that can be changed by passing an electric current through it is called Secondary Cell. The chemical reaction in this case is reversible.

14. Fused Plug
It is a wired plug, which has its own cartilage fuse. It is used in a ring main circuit.

15. Electric Circuit
A combination of electrical components that form a conducting path is called an electric circuit.

16. Commercial Unit of Energy (kWh)
1 kWh is the energy produced by a resistor or conductor in 1 hour when it uses 1000 Watt power.

17. Watt
If 1 joule of electrical work is done in 1 second then the power is called 1 watt.
Electrostatic Induction
When a charged body brought close to another uncharged body then other body gains some chrge without any touch. This is called electrostatic induction.
Gold Leaf Electroscope
An electroscope is a device that can be used for detection of charge.
Construction
It consists of a glass case that contains two turn leaves of gold (Au) which are capable to diverge. The leaves are connected to a conductor to a metal ball or disk out side the case, but are insulated from the case itself.
(Diagram)
Working
If a charged object is brought close to the ball, a separation of charge is induced between the ball and gold leaves. The two leaves become charged and repel each other. If the ball is charged by touching the charged object the whole assembly of ball and leaves acquires the same charge. In either case greater the amount of charge greater would be the diverging in lens.
Electrostatic Potential
A charged body place in electrostatic field as an electrostatic potential as earth has its gravitational potential.
Potential Difference
Definition
“The difference in electrostatic potential between two points in an electrostatic field is called potential difference.”

When a unit positive charge body moves against an electrical field from A to B, then work done has been stored as potential difference. Therefore, we say that
“Potential difference is work done or energy stored per unit charge.”
Unit
Since
Potential Difference = Work Done/Charge
V = W/q
Therefore, its unit is:
V = Joules/Coulomb = J/C = Volt.
Volt
1 volt potential difference is equal to one joule work done on 1 coulomb charge.
Capacitor
It is a device for string electric charge. It is a system of two (or more) plates on which we can store electric charge.
Parallel Plate Capacitor
It is a simple capacitor with two parallel plates on which we store the electric charge.
(Diagram)
Construction
A parallel plate capacitor has two metallic plates with their stands and a dielectric which is air or some insulator. E.g. wax paper, wax, oil and mica.
Working
When the plates of a capacitor are connected to a voltage source. The electrons flow from a plate A to the positive charged terminal and B plate to negative terminal. Thus plate A acquires -q charge. Due to attraction voltage on plates increases gradually. Then charging stops when the potential difference (voltage) becomes the voltage of source.
Capacity or Capacitance
It is the ability of capacitor to store the charge. Charge stored per unit voltage is called capacitance.
Unit
The unit of capacitance is Farad = coulomb/volt.
Farad
If 1 coulomb charge charge produces a potential difference of 1 volt then capacitance is equal to 1 Farad.
Factors
Capacitance of a capacitor depends upon the following factors:

• Area of Plates
• Nature of dielectric
• Distance between plates
• Nature of metal plates
• Temperature of Dielectric and Plates

Electromotive Force (e.m.f)
A measure of the energy supplied by a source of electric current. It is equal to the energy supplied by the source to each unit of charge.
e.m.f = Energy Supplied / Charge
Unit
The unit of e.m.f is volt.
Electric Current
“The rate of flow of charge is called electric current.”
Mathematical Form
According to the definition:
Electric Current = Charge /time
I = q/t
Unit
The unit of current is Ampere (A) = coulomb/sec
Ampere
When one coulomb charge passing through a conductor in one second the current is said to be 1 Ampere.
Resistance
Definition
“The ratio of the potential difference across an electrical element to the current in it is called resistance.”

Resistance measures the opposition of the conductor to the flow of charge.
Unit
The unit of resistance is Ohm.
Factors on which Resistance Depends
Resistance Depends upon the following factors:

• Area of Cross Section of a Conductor: Resistance increases when area of cross section increases.
• Length of Conductor: Resistance increases when the length of conductor is increased.
• Temperature: Resistance in metallic substances is directly proportional to temperature and in non-metals is inversely proportional to the temperature.
• Nature of Substance: Resistance also depends upon the nature of the conductor or substance.

Ohm’s Law
Statement
The current passing through a conductor is directly proportional to the potential difference across the end points of the conductor.
Mathematical Form
According to this law:
V < I (< represents the sign of proportionality. Do not write this in your examination paper) => V = IR
Where R is a constant is called the resistance of the conductor.
Resistor
The body or thing that offers resistance in an electrical circuit is known as resistor. The appliance or device that works on the presence of electric current is known as resistor.
Combination of Resistors
1. In Series
When resistors are combined in series, they have the following properties:

• Current passes through all resistors has equal value, i.e. I = I1 = I2
• Voltage is different according to the resistance.
• Total voltage is equal to the combined voltage or the sum of the voltages of all resistors, i.e. V = V1 + V2 + V3
• Total resistance is equal to the sum of all the resistances, i.e. RE = R1 + R2 + R3

Derivation
(Diagram)
As show in the above diagram and according to the properties of combination.
V + V1 + V2 + V3
but V = IR and V1=IR1, V2=IR2 and V3 = IR3, therefore:
IR(E) = IR1 + IR2 + IR3
IR(E) = I (R1 + R2 + R3)
R(E) = R1 + R2 + R3
2. In Parallel
When resistors are combined in parallel then this combination has the following properties:

• Current has different ways to pass through.
• Current has different value in each resistor according to its resistance.
• Total current is equal to the algebraic sum of each current, i.e.e I = I1 + I2 + I3
• Potential difference (Voltage) is same across each resistor, i.e. V = V1 = V2 = V3
• Resistance is small or less than all combined resistance.
• Total resistance is given by the formula 1/R(E) = 1/R1 + 1/R2 + 1/R3

Derivation
(Diagram)
By the help of properties of parallel combination:
I = I1 + I2 + I3
According to Ohm’s Law, V = IR and I = V/R then we say that:
V/R(E) = V/R1 + V/R2 + V/R3
=> V/R(E) = V (1/R1 + 1/R2 + 1/R3)
1/R(E) = 1/R1 + 1/R2 + 1/R3
Difference between AC and DC
Alternating Current
1. AC is obtained by a resistor that is connected in series with a source of alternating current.
2. Its direction continuously changes.
3. It is obtained by a generator.
4. Its transportation from one point to another point is very easy.
5. It has a frequency about 40 Hz to 60 Hz.
6. No voltage drop takes place in the time of transportation.
7. It is not too dangerous.
8. It is cheaper than DC.
9. It changes very high to low or vice versa.
10. It changes its direction continuously as +y and -y.
Direct Current
1. DC is obtained by connecting the two ends of a conductor to the terminals of a batter.
2. Its direction remains unchanged.
3. It is obtained by a chemical reaction.
4. Its transportation is very difficult.
5. It has no frequency.
6. Great voltage drop takes place in the time of transportation.
7. It is too dangerous.
8. It is expensive.
9. It cannot change easily.
10. It has no direction.
Joule’s Law
Statement
The heat produced by an electric current I, passing through a conductor of resistance R for time t is equal to I2RT. (2 represents power).
The heat produced per unit time in a given conductor is proportional to the square of the current.
Derivation
According to this law:
W < I2t (Here 2 represents the square of current) => W = I2Rt(Here 2 represents the square of current)
Power
The rate of doing work is called Power.
Mathematical Form
P= W/T
=> P = I2Rt/t
=> P = I2R
Substituting the value of I from Ohm’s law in the above equation:
=> P = {V2/R2} R
=> P = V2/R
=> P = V2/V/I
=> P= VI
Difference between Resistance and Conductance
Resistance
1. Resistance is the measure of opposition by the conductor to the flow of charge.
2. It is the reciprocal of the conductance and is measured in volt per ampere or ohm.
Conductance
1. Conductance of a wire is the ease with which current flows in it.
2. It is the ratio of current and potential difference. Its unit is ampere per volt or seimens

Nature of Light and Electromagnetic Spectrum

Definitions 1. Dual Nature of Light
Light has dual nature, it behaves not only as a particle (photon) but also as a wave. This is called dual nature of light.

2. Dispersion of Light
When a beam of sunlight falls on a prism, the light is split up in seven colours. This phenomenon is called Dispersion of Light.

3. Rainbow
The rainbow is an arc of spectral colours formed across the sky during or after rainfall in the morning or when the sun is behind us.

4. Photons (Quantum)
Photons are tiny packets of energy. They behave as particles but actually they are not particles.
Newton’s Corpuscular Theory of Light
This theory which was proposed by Newton is as follows:

• Light is emitted from a luminous body in the form of tiny particles called corpuscles.
• The corpuscles travel with the velocity of light.
• When corpuscles strike the retina they make it sense light.
• Medium is necessary for the propagation of light.
• Velocity of light is greater in denser medium.

Wave Theory of Light
In 1676, Huygen proposed this theory. According to this theory:

• Light propagates in space in the form of waves.
• It can travel in space as well as in a medium.
• Light does not travel in a straight line but in sine wave form.
• Velocity of light is greater in rarer medium.
• Medium is not necessary for propagation.

Quantum Theory of Light
According to this theory of Max Plank:

• Light is emitted from a source discontinuously in the form of bundles of energy called Photons or Quantum.
• It travels in space as well as a medium.
• Speed of light is greatest in space or vacuum.

How A Rainbow is Formed?
As we know a prism disperses sunlight into a series of seven colours. When rain falls, raindrops behave like a prism and white light entering the raindrop splits up into seven colours on refraction. These are appeared as Rainbow.
Spectrum
After the dispersion of light or any electromagnetic wave, a band of colours is formed, which is known as a spectrum.

Electromagnetic Spectrum
Electromagnetic spectrum is a result obtained when electromagnetic radiation is resolved into its constituent wavelength.
Waves of Electromagnetic Spectrum
Radio Waves
It has a large range of wavelengths from a few millimeters to several meters.
Microwaves
These radio waves have shorter wavelength between 1mm and 300 mm. Microwaves are used in radars and ovens.
Infrared Waves
It has a long range. Its mean wavelength is 10 micrometers.
Visible Waves
It has a range of 400 nm to 700 nm.
Ultraviolet Waves
Their wavelength ranges from 380nm onwards. These are emitted by hotter start (about 25000 C)

Refraction of Light and Optical Instruments

Definitions 1. Emergent Ray
The ray after passing the second medium comes again in the first medium. It is called emergent ray.

2. Emergence Angle
The angle formed by the emergent ray and normal is called emergence angle denoted by <e.
3. Optical Center
The middle point of the lens is called optical center. The ray passing through this point does not bend.

4. Accommodation
The ability of the eye to change the focal length of its lens so as to form a clear image of an object on its retina is called is power of accommodation.

5. Persistence of Vision
When an object is seen by an eye, its image forms on retina. If the object is removed, the impression of image persists in the eye for about 1/10 second. This interval is called Persistence of Vision.

6. Power of Lens
The power of the lens is the reciprocal of the focal length measured in meter. Its unit is Dioptre.
Refraction of Light
Definition
“The change in the direction and velocity of light as it enters from one medium to another is known as Refraction of Light.”
Laws of Refraction

• The incident ray, refracted ray and the normal at the point of incidence all lie in the same plane.
• The ratio of sine of angle of incidence (i) to the sine of angle of refraction (r) is constant for all rays of light from one medium to another. This constant is known as Refractive Index (u). This ratio is also equal to the ratio of the speeds of light in one medium to another.

Refractive Index = sin
Refractive Index
The ratio between the sine of the angle of incidence to the sine of angle of refraction is known as Refractive Index.
Refractive Index = sin
Snell’s Law
The refractive index between two particular mediums is equal to the ratio of speed of light in first medium and speed of light in second medium equal to the ratio between sin



Refractive Index = sin
Prism
Definition
“Prism is a transparent piece of glass. It has three rectangular sides and two triangular sides.
Refraction Through a Prism
(Diagram)
where,

• <i = angle of incidence
• <i = angle of refraction
• <e = angle of emergence
• <d = angle of deviation

Total Internal Reflection
(Diagram)
If the value of angle of incidence is increased so much so that it becomes greater than tht of the critical angle then no more refraction occurs but on the other hand refracted ray again comes back in the denser medium. Actually at that time, the surface of denser medium acts as a plane mirror and the incident ray bends in the same medium. This phenomenon is called Total Internal Reflection. It is used in Periscope, Optical Fibers and other instruments.
Total Reflecting Prism
Total internal reflection is used in prism. In prism the angle between two opposite sides is 90 and other two angles are 45 each. If we arrange a ray so that it falls perpendicular to the AB side then it will refract without bending and strike the side AC with angle 45. Then it totally reflects to the side BC.
Conditions for Total Internal Reflection
The ray of light should travel from denser to rarer medium.
The angle of incidence should be greater than the critical angle.
Lenses
Definition
A transparent and smooth glass or any refracting medium surrounded by two spherical surfaces is known as lens.

Types of Lenses
There are two types of lenses:
1. Convex Lens
If the glass is thick at the center and thin at the edges then it is known as convex lens. It is a converging lens.
(Diagram)
It has three types:

• Double Convex Lens
• Plano Convex Lens
• Concavo Convex Lens

2. Concave Lens If the lens is thinner in the center and thicker at the edges then it is known as a concave lens. It is a diverging lens.
(Diagram)
It has three types:

• Double Concave Lens
• Plano Concavo Lens
• Convex Concave Lens

Formation of Image by Convex Lens
1. Object at Infinity
When object is placed at infinite distance from convex lens the rays coming from the object are parallel to each other and they meet after refraction at the focus.
Details of Image

• Formed at Focus
• Real
• Inverted
• At opposite side
• Highly diminished

2. Object Beyond 2F
When object is placed at some distance from 2F then image is formed between the focus and center of curvature (2F).
Details of Image

• Between F and 2F
• Opposite side of Lens
• Real
• Inverted
• Small in size

3. Object at 2F
When object placed at center of curvature, image is formed at center of curvature at the opposite side.
Details of Image

• Real
• Inverted
• At 2F
• Same in size
• At the opposite side of the Lens

4. Object between F and 2F
When object is placed between the focus and center of curvature then the image is formed on opposite side beyond the center of curvature.
Details of Image

• Real
• Inverted
• Large in size
• Opposite side of lens
• Beyond 2F

5. Object at F
When object is placed at focus the refracted rays are parallel to each other and meet at infinity.
Details of Image

• Real
• Inverted
• Extremely Large
• Opposite side of Lens
• At infinity

6. Object between F and O
When object is placed between the lens and principal focus, then the refracted rays does not meet at opposite side but image is formed at the same side where the object is placed.
Details of Image

• Virtual
• Erect
• Large
• Same side of lens
• Beyond the object

Optical Instruments
1. THE EYE
(Diagram)

Functions of the Parts of Eye
1. Sclera Scelortic
It is a layer enclosed in cavity filled with a fluid called Vitrous Humour. It is the outer coating of eye.
2. Choroid
It is a dark membranous coating. This is coated with black pigments. It keeps the inner parts of the eye ball light proof.
3. Retina
It is semi-transparent membranes of nerve fibers forming the innermost coating of the eye and sensitive to light. It is a screen on which image is formed.
4. Cornea
It allows light into the eyes. It is transparent and bulging in shape.
5. Iris
It is like diaphragm of a camera. It has a tiny opening at its center called pupil, which regulates the quantity of light entering the eye.
6. Crystalline Lens
This is a lens that automatically contracts and expands, alters the focal length of eye lens.
7. Ciliary Body
It holds crystalline lens in the proper position.
8. Aqueous Humour and Vitrous Humour
The place between cornea and the lens is filled by a transparent liquid called Aqueous Humour. The large chamber of the eye between the lens and the back of eye is filled with a jelly like substance called Vitreous Humour. These liquids serve mainly to keep the spherical shape of the eye.
Main Defects of Eye
1. Short Sightedness (Myopia)
If a person can see object placed near, but cannot see distant object, this defect is known as short sightedness.
Causes
This defect appears due to increase in thickness of eyeball. The focal length decreases making the image to form before retina.
(Diagram)
Removal of Defect
It is removed by using a concave lens of suitable focal length.
(Diagram)
2. Long Sightedness (Hypermetropia)
If a person can see distant objects, but not near objects, this defect is called long sightedness.
Causes
This defect appears due to decrease in thickness of ball. The focal length increases so that the image is formed beyond the retina.
(Diagram)
Removal of Defect
It is removed by sing a convex lens of suitable focal length.
(Diagram)
3. Astigmatism
It is the defect in which the clear image of an object does not form on the retina.
Causes
This defect appears due to non-sphericity of the cornea.
Removal
This defect can be removed by using lenses of different focal length.
4. Presbyopia
The accommodation power of eye loses by which a person suffers a long sightedness. This defect is called Presbyopia or Lack of Accommodation.
Causes
This defect appears due to loss of accommodation power of the lens of the eye.
Removal
This defect can be removed by using convex lens.
2. CAMERA
Definition
A camera is an optical device for obtaining still photographs or for exposing cinematic films.
Construction
It consists of a light proof box with a lens at one end and a photographic plate or film at other end and a shutter to control the light rays.
Working
To make an exposure, the shutter is opened and an image is formed by lens on the photographic plate or film, small in size. Photographic plate or film saves this image. In this way an image is obtained.
3. COMPOUND MICROSCOPE
Construction
It consist of two convex lenses at the end of two tubes. One tube can slide into other so that the distance between them can be change. The lens near the object is the small convex lens of short focal length is called objective. The lens near the eye is the larger convex of longer focal length is called eyepiece.
(Diagram)
Working
The object is placed between F and @F and its real, inverted and magnified image A’B’ is formed. The eyepiece is brought close to it so that it comes within its focal length. The first image A’B’ acts as an object and a virtual, erect and magnified final image A”B” is formed. The magnification of a microscope can be varied by using different objectives.
4. ASTRONOMICAL TELESCOPE
It is used to see heavenly bodies.
Construction
It consists of two convex lenses at the end of the two metallic tubes. One tube can slide into other so that the distance between can be changed. The lens near the object is a convex lens of longer focal length called the objective, while the lens near the eye is a small convex lens of shorter focal length called the eyepiece.
(Diagram)
Working
The rays from distant object entering the objective and form a real, inverted and diminished image A’B’ near the principal focus. The eyepiece is adjusted so that the image formed by the objective comes within its focal length. Thus the eyepiece acts as a magnifying glass and a virtual, erect and magnified image A”B” is formed by the first image.
Difference between Real Image and Virtual Image
Real Image
1. Real image is formed when rays after reflection actually meet at a point.
2. Real image is inverted and can be seen on a screen.
3. It has a physical existence.
Virtual Image
1. Virtual image is formed when rays do not actually meet but appear to diverge from a point.
2. Virtual image is erect and cannot be seen on a screen.
3. It does not have a physical existence.

Propagation and Reflection of Light

Definitions 1. Incident Ray
The ray that strikes the surface of the medium is known as Incident Ray.

2. Reflected Ray
The ray that is sent back into the same medium after reflection is known as reflected ray.

3. Plane Mirror
A flat smooth reflecting surface, which shows regular reflection is known as plane mirror.

4. Normal
Perpendicular line on the reflecting surface is known as normal.

5. Pole
The centre of the spherical mirror is called pole.
6. Angle of Incidence
The angle subtended by the incident ray to the normal is known as angle of incidence.
7. Angle of Reflection
The angle subtended by the reflected ray to the normal is known as angle of reflection.

8. Center of Reflection
The center of the hollow sphere of which the mirror is a part is called center of curvature.

9. Principle Axis
The straight line passing through center of curvature nad the pole is known as principle axis.

10. Principle Focus
The ray coming parallel to principal axis after converges to or diverges from a point, which is called principle focus.

11. Focal Length
The distance between the principle focus and pole of the mirror is called Focal Length.

12. Radius of Curvature
The distance between the center of curvature and the pole is called radius of curvature.

13. Real Image
The image that can be seen on a screen is known as a real image.

14. Virtual Image
The image that cannot be seen on a screen is known as a virtual image.

15. Magnification
The ratio between the image height and object height is known as magnification.

or
The ratio between the image distance to the object distance is known as magnification.
Reflection of Light
Definition
“The process in which light striking the surface of another medium bounces back in the same medium is known as Reflection of Light.”
Laws of Reflection
1. The angle of reflection, is equal to the angle of incidence: n 2. The incident ray, reflected ray and normal, all lie in the same plane.

Kinds of Reflection
There are two types of Reflection:
1. Regular Reflection
Definition
When parallel rays of light strike a surface and most of them are reflected in a same particular direction or same angle, they are said to be regularly reflected and the phenomenon is known as regular reflection.

Regular reflection occurs when parallel rays of light strike with an ideal smooth plane surface. In regular reflection parallel rays remain parallel after reflection.
(Diagram)
2. Irregular Reflection
Definition
When some rays of light strikes a surface and the reflected rays scatter in different directions, this type of reflection is called irregular reflection.

It occurs when parallel rays strike with an irregular rough surface. In this case rays does not remain parallel after reflection and they scattered.
(Diagram)
Advantages of Irregular Reflection

• Due to this reflection, sunlight reaches us before sunrise and persists for some time even after the sunset.
• Due to this reflection we get sufficient light in our rooms and other places where sunlight do not reach directly.
• Due to this reflection sunlight reaches to each of the leaves of a tree and photosynthesis takes place on large scale.
• Due to this reflection, we can see luminous objects.

Image Formed by a Plane Mirror
Consider a mirror MM’, AP is an object. Consider that a point P lies on the tip of the object. From P as ray travels and strikes mirror and reflect back to the eye, they appear to come back. From Point P’ as shown in the figure. Hence P’ is the image of P. Similarly, infinite points lying an object produces infinite images of points and complete image of an object is formed.
Characteristics of Image Formed by a Plane Mirror

• Image is same in size as that of the object.
• The distance of object and image are equal from the mirror.
• The image formed is virtual and inverted.

Spherical Mirrors
Definition
“A spherical mirror is a section of a of a hollow sphere.”

Types of Spherical Mirrors
There are two types of spherical mirror:
1. Concave Mirror (Converging Mirror)
2. Convex Mirror (Diverging Mirror)
1. Concave Mirror
Definition
“The spherical mirror in which inner side of the surface is polished for reflection is called a concave mirror.”
Properties

• The bulging side is polished.
• Reflection occurs from its hollow side.
• They converge the parallel rays at a point.
• They can form real and imaginary, both types of images.

2. Convex Mirror
Definition
“The spherical mirror in which inner side of the surface is polished for reflection is called concave mirror.”
Properties

• The bulging side is polished.
• Reflection occurs from its hollow side.
• They converge the parallel rays at a point.
• They can form real and imaginary, both type of images.

Formation of Image by Concave Mirrors
There are six cases to form an image by concave mirror.
1. Object at Infinity
(Diagram)
If the object is placed at infinity from the mirror, the rays coming from the object are parallel to principal axis. After reflection, they meet at principal focus and image is formed at the focus.
Details of Image

• Formed at F.
• Extremely Small
• Real
• Inverted

2. Object Beyond C
(Diagram)
If the object is placed beyond C, rays coming from the object are not parallel. They meet after reflection between the focus and center of curvature. Therefore, image is formed between the focus and center of curvature.
Details of Image

• Formed between F and C.
• Small in size.
• Real
• Inverted

3. Object at Center of Curvature ‘C’
When object is placed at the centre of curvature, the image formed at the same place.
(Diagram)
Details of Image

• Formed at C
• Equal in size
• Real
• Inverted

4. Object Between F and C
(Diagram)
When the object is placed between the focus and Centre of curvature, the image is formed beyond the centre of curvature.
Details of Image

• Formed beyond C.
• Large in size.
• Real
• Inverted

5. Object at F
(Diagram)
When object is placed at focus the reflected rays become parallel to each other. The two parallel lines meet at infinity. Therefore, we say the image is formed at infinity.
Details of Image

• Formed at Infinity.
• Extremely Large
• Real
• Inverted

6. Object between P and F
(Diagram)
For locating object between pole and focus the rays reflected do not meet because they diverge. But they meet backward. So, the image is formed backward or behind the mirror.
Details of Image

• Formed behind the mirror.
• Large in size
• Virtual
• Erect

Uses of Spherical Mirror
Spherical mirrors are used in several places. Some of them are given below:
Shaving: A concave mirror is used to enlarge the image.
Microscope: A convex mirror is used for magnification in a microscope.
Telescope: The convex mirror is used.
In Searchlights and Headlights: Concave mirror is used to form the rays in searchlights and headlights, used for different purposes.
For Rear View: The convex mirror is used in automobiles.
In Medical Examination (Opthalmoscope): Doctors use concave mirror for the examination of ear, nose, throat and eyes of patients