Two coils ‘1’ and ‘2’ are placed close to each other as shown in the figure. Find the direction of induced current in coil ‘1’ in each of the following situations, justifying your answers: (a) Coil ‘2’ is moving towards coil ‘1’. (b) Coil ‘2’ is moving away from coil ‘1’. (c) The resistance connected with coil ‘2’ is increased keeping both the coils stationary.
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Always apply Lenz’s Law: the induced current in a coil will oppose the change in magnetic flux. Approaching magnets or increasing currents lead to opposing induced fields; receding magnets or decreasing currents lead to supporting induced fields.
(a) \underline{Coil ‘2’ is moving towards coil ‘1’:}
As coil 2 approaches coil 1, the magnetic flux linked with coil 1 increases due to the increasing proximity of the magnetic field of coil 2. According to Lenz’s Law, coil 1 will produce an induced current that opposes the increase in magnetic flux. This means the induced current in coil 1 will produce a magnetic field that opposes the field of coil 2. Direction: The induced current in coil 1 will be in the anticlockwise direction when viewed from the right side (i.e., from P to O). (b) \underline{Coil ‘2’ is moving away from coil ‘1’:}
As coil 2 recedes, the magnetic field and hence the magnetic flux linked with coil 1 decreases. Lenz’s Law tells us that coil 1 will oppose this decrease by inducing a current that tries to maintain the flux (i.e., in the direction of the original field). Direction: The induced current in coil 1 will be in the clockwise direction (i.e., from O to P). (c) \underline{Resistance in coil ‘2’ is increased (coils stationary):}
An increase in resistance in coil 2 reduces the current in it, which decreases its magnetic field. This decrease in flux through coil 1 causes an induced current in coil 1 to oppose this reduction (as per Lenz’s Law). Direction: The induced current in coil 1 will again be in the clockwise direction (i.e., from O to P).
