Answer
a. Direction a to b.
b. Direction b to a.
c. Direction b to a.
Work Step by Step
By Lenz’s Law, the field caused by the induced current is directed to oppose the change in flux.
a. With switch S closed, the magnetic field of coil A is to the right, where coil B is located. When the switch is opened the magnetic field decreases rapidly. The field of the current induced in coil B is to the right, to fight the decrease in the flux. By the right hand rule, the current in the circuit flows through the resistor in the direction a to b.
b. With switch S closed, the magnetic field of coil A is to the right, where coil B is located. When coil B is moved as described, the magnetic field it feels will increase, and so will the flux. The field of the current induced in coil B is to the left, to fight the increase in the flux. By the right hand rule, the current in the circuit flows through the resistor in the direction b to a.
c. With switch S closed, the magnetic field of coil A is to the right, where coil B is located. If the resistance R decreases as described, the magnetic field at coil B’s location will increase, and so will the flux. The field of the current induced in coil B is to the left, to fight the increase in the flux. By the right hand rule, the current in the circuit flows through the resistor in the direction b to a.
