Question

A metallic ring connected to a rod oscillates freely like a pendulum. If now a magnetic field is applied in the horizontal direction so that the pendulum now swings through the field, the pendulum will

• A. keep oscillating with old time period
• B. keep oscillating with smaller time period
• C. keep oscillating with larger time period
• D. come to rest rapidly

Answer 1

The correct option is D

come to rest rapidly

1. As soon as the ring will enter the magnetic field, an EMF will be induced in the ring.
2. This EMF will be induced due to the faradays law of electromagnetic induction.
3. Faraday's law of electromagnetic induction states that whenever we place a conductor in a varying magnetic field, an electromotive force (EMF) is induced.
4. Also, if the conductor circuit is closed, a current is induced in it, which is called induced current.
5. Lenz's law states that the current induced in a circuit due to a change in a magnetic field is always directed to oppose the change in flux and to exert a mechanical force that will oppose the motion.
6. Thus the induced EMF in the ring will oppose the motion of the ring.
7. As the ring is made up of metal; it should have some resistance in it.
8. Due to both EMF opposition and resistance, the energy of the ring will slowly decrease and the ring will come to rest very soon.

Thus, the correct option is option D.