The circuit below contains three 100-W light bulbs and a capacitor. The emf ε = 110V. At the instant the switch S is closed, which light bulb is brightest?
A) A
B) B
C) C
D) A and B
E) All three are equally bright.

Question

The circuit below contains three 100-W light bulbs and a capacitor. The emf ε = 110V. At the instant the switch S is closed, which light bulb is brightest? 
A) A 
B) B 
C) C 
D) A and B 
E) All three are equally bright.

Quizplus · Accepted Answer

When the switch is first closed, the capacitor acts like an open circuit because it is uncharged, so no current flows through the circuit. As the capacitor charges up, the amount of current flowing through the circuit increases. The 100-W bulbs all have the same resistance, so they will all have the same brightness when the circuit reaches steady state. However, since bulb C is further from the capacitor than bulbs A and B, it will take longer for the capacitor to charge up to the point where the bulbs are all equally bright. Therefore, at the instant the switch is closed, bulb C will be the brightest.

The Circuit Below Contains Three 100-W Light Bulbs and a Capacitor