Question

A long solenoid of radius .10 m has 5000 turns and a length of .50 m. A separate conducting ring of resistance 5.0 ? and radius .025 m is placed concentrically and coaxially in the middle of the solenoid. The solenoid is turned on and a current of 2.5 A is produced. a) Sketch the situation. b) Does a current flow in the ring at any time? Explain. c) If the solenoid is switched on in a time of .025s, find the average current in the ring. d) On your sketch indicate the direction of the current in the solenoid and the direction of the current in the ring. (Useful info: The B-field of a solenoid is given by B = ?0ni) .

Answer 1

a)

b)

the current flows in the ring as soon as the solenoid is turned on and the current in it changes from 0 A to 2.5 A. once the current in solenoid becomes steady , it stops changing the magnetic flux linked with the ring. hence no current flows in the ring once the current in it becomes steady

c)

B = change in magnetic field = n i = (12.56 x 10^-7) (5000/0.50) (2.5) = 0.0314 T

t = time taken = 0.025 sec

A = area of the ring = r² = (3.14) (0.025)² = 0.0019625 m²

average current is given as

i = BA/(tR)

i = (0.0314) (0.0019625)/(0.025 x 5)

i = 0.00049298 A