Electromagnetic Induction — Physics STD 12 Science — Question

Currents can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such currents flow in the from of irregularly shaped loops throughout the body of the metal. These currents look like eddies or whirlpools in water so they are known as eddy currents. Eddy currents have both undesirable effects and practically useful applications. For example it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers.

1. The working of speedometers of trains is based on:

1. Wattless currents.
2. Eddy currents.
3. alternating currents.
4. pulsating currents.

2. Identify the wrong statement.

1. Eddy currents are produced in a steady magnetic field.
2. Induction furnace uses eddy currents to produce heat.
3. Eddy currents can be used to produce braking force in moving trains.
4. Power meters work on the principle of eddy currents.

3. Which of the following is the best method to reduce eddy currents?

1. Laminating core.
2. Using thick wires.
3. By reducing hysteresis loss.
4. None of these.

4. The direction of eddy currents is given by:

1. Fleming's left hand rule.
2. Biot-Savart law.
3. Lenz's law
4. Ampere-circuital law.

5. Eddy currents can be used to heat localised tissues of the human body. This branch of medical therapy is called:

1. Hyperthermia.
2. Diathermy.
3. Inductothermy.
4. None of these.