Question

The parallel plates of capacitor are charged to a potential difference of 320 volts and are then connected across a resistor. The potential difference across the capacitor decays exponentially with time. Alter 1 second the potential difference between the plates of the capacitor is 240 volts then after 2 seconds the potential difference between the plates will be –

• A. 200 V
• B. 180 V
• C. 160 V
• D. 140 V

Answer 1

Answer: (B)

180 V

Answer 2

V = V₀e^–t/Rc; 240 = 320 e^–1/Rc; $\frac { 3 } { 4 }$ = e^–1/Rc

V = V₀e ^–2/Rc ; V = 320 (e^–1/Rc)² = 320 × $\frac { 9 } { 16 }$ = 180 V