A lightbulb is plugged into a household outlet, and one of the wires leading to it is wound into a coil. Now a slug of iron is slid into the coil. What effect will this have?
A) The lamp will get brighter because there will be an induced emf that will drive more current through the lamp.
B) The lamp will dim because a back emf will be produced by the coil, and this will reduce the current flowing in the coil and the lamp.
C) This will have no effect on the brightness of the lamp.
D) The lamp will dim because energy will now be dissipated in the iron.
E) This will not affect the lamp's brightness because the coil will shift the phase, but not the magnitude, of the current through the lamp.

Question

Quizplus · Accepted Answer

Inserting an iron slug into the coil increases the coil's inductance, which in turn induces a back electromotive force (emf) when the current through the coil changes. This back emf opposes changes in the current, effectively reducing the current flowing through the circuit and thus dimming the lamp.

A Lightbulb Is Plugged into a Household Outlet, and One