Question

A battery is connected to a resistor and an uncharged capacitor. The switch for the circuit is closed at t = 0 s. (Assume all circuit elements are connected in series.)

(a) While the capacitor is being charged, which of the following is true?

A. Current through and voltage across the resistor decrease.

B. Current through and voltage across the resistor first increase and then decrease.

C. Current through and voltage across the resistor first decrease and then increase.

D. Current through and voltage across the resistor increase.

(b) When the capacitor is fully charged, which of the following is NOT zero?

A. voltage across the resistor

B. current in the resistor

C. current in the capacitor

D. none of the above

Answer 1

The capacitor will charge up gradually through the resistor until the voltage across it reaches that of the supply voltage and charging current decreases exponentially.  At infinity, the charging current finally diminishes to zero and the capacitor acts like an open circuit.

(a)Hence current through and voltage across the resistor(V=IR) decrease during charging of the capacitor.

(b) When the capacitor is fully charged( t = ∞), Charging current in the circuit is I = 0.

Hence voltage across the resistor=IR = 0

current in the resistor I =0

current in the capacitor I =0

voltage across the capacitor as Vc = Supply voltage(Vs).

So, None of these is the correct option(D)