Two bulbs are shown in a circuit that surrounds a region of increasing magnetic field directed out of the page. When the switch is closed,
A) bulb 1 glows more brightly.
B) bulb 2 glows more brightly.
C) both bulbs continue to glow with the same brightness.
D) bulb 1 goes out.
E) bulb 2 goes out.

Question

Two bulbs are shown in a circuit that surrounds a region of increasing magnetic field directed out of the page. When the switch is closed, 
A) bulb 1 glows more brightly. 
B) bulb 2 glows more brightly. 
C) both bulbs continue to glow with the same brightness. 
D) bulb 1 goes out. 
E) bulb 2 goes out.

Quizplus · Accepted Answer

The increasing magnetic field induces an EMF in the loop of wire of the circuit, which in turn causes a current to flow through the bulbs. The brightness of a bulb is related to the current flowing through it. Bulb 1 has more resistance than bulb 2, so it will experience a greater voltage drop and a smaller current. As the magnetic field increases, the induced EMF in the circuit increases, causing the current to increase. Eventually, the current flowing through bulb 1 becomes so small that it goes out, while bulb 2 continues to glow with a higher current.

Two Bulbs Are Shown in a Circuit That Surrounds a Region