Nuclear Physics | X – Class Physics Notes

Chapter-19

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.

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Electronics | X – Class Physics Notes

Chapter-18

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.

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Magnetism and Electromagnetism | X – Class Physics Notes

Chapter-17

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

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