In the figure, a bar magnet moving towards the right or left induces an emf in the coils (1) and (2). Giving reasons, find the directions of the induced currents through the resistors AB and CD when the magnet is moving (a) towards the right, and (b) towards the left.
Solution
By Lenz's law each coil opposes the change in flux produced by the approaching or receding pole. (a) When the magnet moves to the right, the near face of coil (1) is approached by a pole and the near face of coil (2) recedes; the coils develop poles that oppose the motion, and tracing the induced currents gives flow from B to A in the resistor of coil (1) and from C to D in the resistor of coil (2). (b) When the magnet reverses and moves to the left, both induced effects reverse, so the current is from A to B in coil (1) and from D to C in coil (2). In every case the induced current direction is fixed by opposing the change in flux.
