Question

A magnet is dropped down an infinitely long vertical copper tube(a) The magnet moves with continuously increasing velocity and ultimately acquires a constant terminal velocity(b) The magnet moves with continuously decreasing velocity and ultimately comes to rest(c) The magnet moves with continuously increasing velocity but constant acceleration(d) The magnet moves with continuously increasing velocity and acceleration

Answer 1

answer : option (A)

explanation : if A bar magnet is falling vertically down through the hollow region of copper tube, then magnetic flux linked with the copper tube changes and hence, eddy currents are generated in the body of the tube .

according to Lenz's law, eddy currents oppose the falling of magnetic bar due to this bar magnet experiences retarding force. here retarding force depends on velocity of magnet. when velocity of bar magnet increases, retarding force also increases and finally retarding force equals weight of bar magnet. Then, magnet attains constant terminal velocity. e.g., bar magnet ultimately fall with zero acceleration .

hence, when a bar magnet is dropped down an infinitely long vertical copper tube, then magnet moves with continuously increasing velocity and ultimately acquires a constant terminal velocity.