f.5 physics magnetism

Q: what happen to the golden ring when the switch is closed? explain

A: When the switch is closed, current flows through the coil. By using right hand grip rule, the end nearest to the golden ring becomes the "north" pole. As such, magnetic field lines build up through the golden ring. By Faraday's Law, induced emf, and hence curen,t produced in the ring. Because of Lenz's Law, the side of the ring facing the coil becomes "north" pole. As a result, the ring is observed to repel from the coil.

Q: the switch remains closed. what happen to the ring if the slide contact of the rheostat, i) is kept at A

A: When the contact is kept at A, the current through the coil remains constant. There is no change of magnetic flux through the coil and the golden ring. No induced current is produced in the ring. Hence, the repulsive force acting on the coil disappears.

Q: ii) moves from A to B

A: When the sliding contact moves from A to B, the current flows through the coil decreases. This causes the magnetic flux through the golden ring to decrease. Current is induced again in the ring. By Lenz's Law, the side of the ring facing the coil becomes "south" pole. The ring is thus attracted towards the coil.

Q: iii) oscillates to and fro between A and B continuously with 1 Hz ?

A: The current flows through the coil increases and decreases alternatively with a frequency of 1 Hz. Thus the magnetic flux through the ring also increases and decreases correspondently. The magnetic polarity of the ring thus alternates between "north" and "south" poles, causing the ring to oscillate at 1 Hz frequency.