What will happen to the brightness of the light bulb as the iron core is moved away from the wire coil in this circuit? Explain why this happens.
The light bulb will glow brighter when the iron core is moved away from the wire coil, due to the change in inductive reactance (XL).
Follow-up question: what circuit failure(s) could cause the light bulb to glow brighter than it should?
One direction you might want to lead your students in with this question is how AC power may be controlled using this principle. Controlling AC power with a variable reactance has a definite advantage over controlling AC power with a variable resistance: less wasted energy in the form of heat.