Using Lenz's law, determine the direction of the current in resistor `ab` in Fig. 3.23 when

(a) switch `S` is opended after having been closed for several minutes.
(b) coil `B` is brought closer to coil `A` with the swich closed. ltbr. ( c) the resistance of `R` is decreased while the switch remains closed.

Explanation

(a) When the switch is opened, the magnetic field to the right decreases. Therefore, the secound coil's induced current produces its own field to the right. That means the current must pass through the resister from point `a` to point `b`.
(b) If coil `B` is moved closer to coil `A`, more flux passes through it towards the right. Therefore, the induced current must produce its own magnetic field to the left to oppose the increased flux. that means the current must pass through the resister from point `b` to point `a`.
( c) If the variable resister `R` is decreased, then more current flows through coil `A`, and so a stronger magnetic field is produced, leading to more flux to the right through coil `B`. the induced current must produced its own magnetic field to the left to oppose the increased flux. That means the current must pass through the resister from point `b` to point `a`.