A light bulb is connected in the circuit shown in the figure with the switch S open and the capacitor uncharged. The battery has no appreciable internal resistance. Which one of the following graphs best describes the brightness B of the bulb as a function of time t after closing the switch?
A) 1
B) 2
C) 3
D) 4
E) 5

Question

A light bulb is connected in the circuit shown in the figure with the switch S open and the capacitor uncharged. The battery has no appreciable internal resistance. Which one of the following graphs best describes the brightness B of the bulb as a function of time t after closing the switch?  
A) 1 
B) 2 
C) 3 
D) 4 
E) 5

Quizplus · Accepted Answer

When the switch is closed, the capacitor will begin to charge and the voltage drop across the bulb will decrease, causing the brightness to decrease as well. As time goes on, the voltage drop across the capacitor will increase and the voltage drop across the bulb will also increase, causing the brightness to increase until it reaches its maximum when the capacitor is fully charged. Option B shows this behavior, where the brightness initially decreases and then increases to its maximum. Options A, C, and D show monotonic increase or decrease in brightness, which is not possible in this circuit. Option E shows an initial increase in brightness followed by a decrease, which is also not possible in this circuit.

A Light Bulb Is Connected in the Circuit Shown in the Figure