Question

The diagram below shows two circular loops of wire (A and B) centred on and perpendicular to the X-axis and oriented with their planes parallel to each other. The Y-axis passes vertically through loop A (dashed line). There is a current I_B in loop B as shown in the diagram. Possible actions which we might perform on loop A are

(I) move A to the right along X-axis closer to B

(II) move A to the left along X-axis away from B

(III) as viewed from above, rotate A clockwise about Y-axis

(IV) as viewed from above, rotate A anti-clockwise aboutY-axis

Which of the actions will induce a current in A only in the direction shown?

(a) Only (I)

(b) Only (II)

(c) Only (I) and (IV)

(d) Only (II) and (III)

Answer 1

Answer is : (a) Only (I)

Current in loop is shown anti-clockwise.

Hence to induce a anti-clockwise current in A, flux going into A must be increased and by bringing A closer to B, we get a anti-clockwise current in A. This is in accordance with Lenz’s law.