Physics Questions and Answers – Electromagnetic Induction – Eddy Currents

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electromagnetic Induction – Eddy Currents”.

1. Name the current induced in solid metallic masses when the magnetic flux threading through them changes.
a) Ampere currents
b) Faraday currents
c) Eddy currents
d) Solenoidal currents
View Answer

Answer: c
Explanation: Eddy currents are the currents induced in solid metallic masses when the magnetic flux threading through them changes. These currents look like eddies or whirlpools in water and so they are known as eddy currents.
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2. Identify the type of commercial motor which works as a consequence of eddy currents.
a) Compressors
b) Induction motors
c) Turbines
d) Hydropowered motors
View Answer

Answer: b
Explanation: A rotating magnetic field is produced employing two single-phase currents. A metallic rotor placed inside the rotating magnetic field starts rotating due to large eddy currents produced in it. These motors are commonly used in fans.

3. Which of the following is not an application of eddy currents?
a) Ammeter
b) Dead beat galvanometer
c) Speedometer
d) Energy meters
View Answer

Answer: a
Explanation: Although eddy currents are undesirable, still they find applications in the following devices: Induction furnace, Electromagnetic damping, Electric brakes, Speedometers, Induction motor, Electromagnetic shielding, and energy meters.
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4. What is measured by the eddy currents induced in energy meters?
a) Electric potential
b) Electric induction
c) Electric power
d) Electric energy
View Answer

Answer: d
Explanation: In energy meters used for measuring electric energy, the eddy currents induced in an aluminum disc are made use of. Therefore, electric energy is measured by the eddy currents induced in energy meters.

5. Eddy currents can be used to heat localized tissues of the human body. What is this branch of science referred to as?
a) Inductology
b) Eddy dynamics
c) Inductothermy
d) Eddy mechanics
View Answer

Answer: c
Explanation: Eddy currents can be used to heat localized tissues of the human body. This branch is called inductothermy. Inductothermy is a method of electrotherapeutics in which certain parts of the body of the patient are heated by an alternating, predominantly high-frequency electromagnetic field, which induces eddy currents in body tissues.
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6. Eddy currents may not be suitable for electrostatic shielding.
a) True
b) False
View Answer

Answer: b
Explanation: No, Eddy currents can be used for electromagnetic shielding. Electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. The higher the conductivity of the sheet used, the better the shielding of the transient magnetic field.

7. ‘X’ set up in the drum exert a torque on the drum to stop the train. Identify X.
a) Induction
b) Eddy currents
c) Electromagnetic oscillations
d) Air pressure
View Answer

Answer: b
Explanation: A strong magnetic field is applied to the rotating drum attached to the wheel. The eddy currents set up in the drum exert a torque on the drum to stop the train. That is the reason eddy currents are set up in the drum of the train wheel.
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8. Identify the law which is used to find out the direction of eddy currents.
a) Lenz’s law
b) Faraday’s law
c) Ampere circuital law
d) Maxwell’s law
View Answer

Answer: a
Explanation: Eddy currents are the currents induced in solid masses when the magnetic flux threading through them changes. Eddy currents also oppose the change in magnetic flux, so their direction is given by Lenz’s law.

9. How can electromagnetic damping be increased?
a) Increasing the magnetic density
b) Reduce viscosity
c) Winding the coil on the aluminum frame
d) Increase the temperature of the coil
View Answer

Answer: c
Explanation: The electromagnetic damping can be increased by winding the coil on a lighter copper or aluminum frame. As the frame moves in the magnetic field, eddy currents are set up in the frame which resists the motion of the coil.
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