1. Which are the factors affect the strength of a solenoid's magnetic fields?

1. No. of turns of coils per unit length.
2. Magnitude of current flowing through the solenoid.

2. What is an electromagnet?

A magnet produced by the flow of electric current in a wire is called an electromagnet. The magnetic strength of an electromagnet depends upon the value of current flowing through the wire. Electromagnets are not magnetic all the time. Once you stop the flow of electricity, it is just a wire again.

3. Mention the uses of electromagnets.

1. Electromagnets are used in loudspeakers, televisions, fans, toys, electric motors etc.
2. Large electromagnets are used to lift heavy cargo iron containers. It is also easy to put these containers at the desired place by putting off the electric current.
3. Horseshoe-shaped electromagnets are used in making electric door bells.

4. What are the parts of an electric door bell?

1. Horseshoe electromagnet
2. Armature
3. Contact spring
4. Contact screw
5. Switch
6. Battery
7. Hammer and gong

5. What is meant by an Armature?

Armature is one of the main parts of an electric door bell. It is a soft iron bar. It is attached to the contact spring suspended from pivot.

6. Explain about Hammer and gong.

A hammer made up of steel is attached to the armature. The gong made of metal (brass or iron) is fixed on a wooden or plastic board. When the switch is pressed, the hammer repeatedly strikes the gong to made a sound.

7. Explain electromagnetic induction.

The phenomenon of inducing an electric current in a closed electric circuit due to changing magnetic field around it is called electromagnetic induction.

8. Which are the factors that affect the strength of the induced current produced by electromagnetic induction?

1. No. of turns in the closed coil.
2. Strength of the magnetic field of the magnet.
3. Relative speed of the movement of magnet and closed coil.

9. We get a.c through the electric wires in our house. But some of our home appliances works only in d.c. How it is possible?

The voltage supply provided in our houses from the electricity pole through electric wires is an a.c voltage of 220 V at 50 hertz frequency. But the devices like television, computer, radio, mobile phones etc. work on direct current. Inside these devices having rectifiers and filters for converting a.c signal to d.c signal.

10. Differentiate between direct current and alternating current.

Direct Current

1. It is a current of constant magnitude.
2. Small magnitude d.c currents are not harmful when pass through human body.

A.C

1. It is a current of changing magnitude.
2. Even small magnitude a.c currents give electric shock when passes through human body.

11. Why dynamo called as an electric generator ?

A dynamo is a device that produce electric current. It is also called an electric generator, because it converts mechanical energy into electrical energy.

12. Explain the working of dynamo ?

A dynamo consists of a coil of conducting wire that is rotated by some mechanical means in between the poles of a magnet. Due to the rotation of the coil, the magnitude of magnetic field passing through it changes. It induces an electric current in the coil by electromagnetic induction process.

13. What is a transformer?

Transformer is a device, which works on the principle of electromagnetic induction to change the supplied a.c voltage to the desired higher or lower level.

14. Write about the types of transformers?

There are two types of transformers

1. Step-up transformer
2. Step-down transformer

The transformers, which increase the voltage level of supplied a.c voltage, are called step-up transformers. For example, if an electrical device works at 350 volts then step-up transformer will increase the voltage of a.c mains from 220 volts to 350 volts.
Those transformers which decrease the voltage level of the supplied, a.c voltage are called step-down transformaers. Example, if an electrical devices works at 150 V then step down transformer will decrease the voltage of a.c mains.

15. Explain about the construction of a transformer.

A transformer consist of a rectangular laminated iron core made up of large number of soft iron plates. Plates are insulated from each other. Two coils of insulated copper wire are wound on two opposite sides of the rectangular laminated iron core. One coil is attached to the a.c mains. It is referred as primary coil. The secondary coil is attached to the load.

16. Which are the factors depend on induced emf on the secondary coil?

The value of induced voltage in the secondary coil depends on two factors:

1. The no. of turns in the secondary coil with respect to that in the primary coil.
2. Voltage supplied to the primary coil.

17. Explain about electric motor.

An electric motor is an electrical device that converts electrical energy to mechanical motion. Its construction is almost similar to that of a dynamo, which does the reverse operation of converting mechanical energy to electrical energy.

18. What is the principle of electric motor?

An electric motor works on the principle that a current carrying conductor experiences a force when placed in a magnetic field. A rectangular coil of wire is kept between the poles of a magnet. A current source is connected between two free ends of the coil. An axle is also connected to the coil. When current passes through the rectangular coil, it starts rotating because opposite arms of the coil experience forces in opposite direction. This produces rotation in the axle.

19. What are the applications of electric motor?

1. Electric motor is used in electric fans to rotate its blades.
2. Used in industrial machines, and many more devices, like washing machines, water lifting pumps and water cooler pumps, for causing rotation of various parts of these devices.