Conceptual Questions Based on Electromagnetic Induction

Q.1. Will an induced emf develop in a conductor, when moved in a direction parallel to the magnetic field ?

Solution. No, because the magnetic flux linked with the conductor does not change when it is moved parallel to the magnetic field. Moreover, the magnetic Lorentz force on the free electrons of the conductor is zero, so no emf is induced across the ends of the conductor.

Q.2. What is the basic cause of induced emf ?

Solution. The basic cause of induced emf is the change of magnetic flux linked with a circuit.

Q.3. Induced emf is also called back emf. Why?

Solution. It is because induced emf always opposes any change in applied emf.

Q.4. A train is moving with uniform speed from north to south, (i) Will any induced emf appear across the ends of its axle ? (ii) Will the answer be affected if the train moves from east to west ?

Solution. (i) Yes, emf will appear because the axle is intercepting the vertical component of the earth’s magnetic field, (ii) No, here also the axle intercepts the vertical component of the earth’s magnetic field, so emf is induced across the ends of the axle.

Q.5. A wire kept along the north-south direction is allowed to fall freely. Will an emf be induced in the wire ?

Solution. No, because neither horizontal nor vertical component of earth’s magnetic field will be intercepted by the falling wire.

Q.6. Predict the polarity of the plate A of the capacitor, when a magnet is moved towards it, as shown in Figure.

Solution. When N-pole of the magnet is moved towards the loop, current is induced in the anticlockwise direction when seen from the magnet side. So the plate A has +ve polarity and the plate B has -ve polarity.

Q.7. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends ? Justify your answer.

Solution. Yes, because the horizontal component of earth’s magnetic field is intercepted by the rod.

Q.8. A vertical metallic pole falls down through the plane of the magnetic meridian. Will any emf be produced between its ends ? Give reason for your answer.

Solution. No emf will be induced because the metallic pole neither intercepts the horizontal component B_H nor the vertical component By of earth’s magnetic field.

Q.9. Does the change in magnetic flux induce emf or current ?

Solution. The change in magnetic flux always induces emf. However, the current is induced only when the circuit is closed.

Q.10. A cylindrical bar magnet is kept along the axis of a circular coil. Will there be a current induced in the coil if the magnet is rotated about its axis ? Give reason.

Solution. No, because the magnetic flux linked with the circular coil does not change when the magnet is rotated about its axis.

Conceptual Questions Based on Electromagnetic Induction

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