Question

Suppose that a copper wire loop is placed in the magnetic field of a solenoid. For each situation below, determine (i) whether or not there is a current induced in the wire loop. If a current is induced, (ii) give its direction according to an observer looking at the setup from the right, (iii) state whether the loop is attracted towards or repelled from the solenoid, and (iv) state whether the force exerted on the loop tends to increase or decrease the relative motion (aka velocity) between the loop and solenoid. Figure 1 (a) The loop is stationary (b) The loop is moving towards the solenoid (c) The loop is moving away from the solenoid

Answer 1

(a)

When the loop is stationary

(i) Induced current - No, there is no induced current because the magnetic field flux through the wire does not change;the number of magnetic field lines in the area of the loop is the same

(ii) No direction

(iii) no movement

(iv) no force

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(b)

loop is moving towards the solenoid

(i) As the loop moves closer to the solenoid the magnetic field lines get closer together. In other words the magnetic field flux is increasing, so current will be induced

(ii) clockwise. Using right hand rule, induced magnetic field is to the left.

(iii) repulsion will take place

(iv) force will decrease

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(c)

loop is moving away from solenoid

(i) As the loop moves away from solenoid the magnetic field lines get further apart means flux decreases so induced field is setup to the right.  so current will be induced

(ii) counter clockwise

(iii) attraction

(iv) decrease