Figure 34 - 26 shows a copper ring that is hung from a ceiling by two threads. D

Question

Figure 34 - 26 shows a copper ring that is hung from a ceiling by two threads. Describe in detail how you might most

effectively use a bar magnet to get this ring to swing back and forth.

http://imageshack.us/photo/my-images/841/skjy.jpg/

A current is sent through a vertical spring from whose lower end a weight hanging. What will happen?

shows a copper ring that is hung from a ceiling by two threads. Describe in detail how you might most effectively use a bar magnet to get this ring to swing back and forth. A current is sent through a vertical spring from whose lower end a weight hanging. What will happen?

Explanation / Answer

Whenever we move a bar magnet along the axial direction of the ring, the magnetic lines of forces of the bar magnet were allowed to pass through the ring which flows from north to south pole of the magnet.

in any situation when we try to take the magnet near the ring(North pole facing the ring) the magnetic field in the ring incereases, and an induced magnetic field will be produced in the ring and now a induced current produces in the ring in the decresing direction of changing magnetic field. i.e., whenever you move the bar magnet away from you towards the ring with the north pole of the magnet facing towards the ring, an induced current is produced in the ring in anti-clock wise direction.

now this current carrying ring acts like an magnet with north pole on the front side and south pole at back side.

and when you move the bar magnet towards the ring it will repel as like poles are moving nearer and the ring moves backward.

similar kind of situation occurs when we move the magnet away from the ring, but produces an clockwise current giving rise to a south pole on the front side of the ring and attracting to the north pole of the magnet and moving forward.

similar kind of situation occurs with the north pole

When current is supplied in a spring with a mass attached at the bottom, just after switching ON the current supply, the magnetic field in the spring increases, as a result spring tries to oppose this change in the magnetic field by reducing the circular area of the spring(i.e., in this process the length of the spring increases as a result of decreasing circular area) and the weigth comes down.

similarly when you suddenly switch OFF the current supply to the spring the weight moves up

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