Question

A capacitor of capacitance C is charged to a constant potential difference V and then connected in series with an open key and a pure resistor R. At time t = 0, the key is closed. If I is current at time t = 0, a plot of log I against t is shown as in the graph (1). Later one of the parameters, i.e. V, R and C is changed, keeping the other two constant and graph (2) is recorded. Then –

• A. C is reduced
• B. C is increased
• C. R is reduced
• D. R is increased

Answer 1

Answer: (B)

C is increased

Answer 2

It is discharging of capacitor

I = $\frac { E } { R } e ^ { - t / R C }$

log I = log– $\frac { \mathrm { t } } { \mathrm { RC } }$

Intercept is constant Ž E & R constant

Slope decrease Ž C ↑