Question
Two identical capacitors $A$ and $B$ are charged to the same potential $V$ and are connected in two circuits at $t = 0$, as shown in figure. The charge on the capacitors at time $t = CR$ are respectively
✓
Answer
(b) Time $t = CR$ is known as time constant. It is time in which charge on the capacitor decreases to $\frac{1}{e}$ times of it’s initial charge (steady state charge).
In figure $(i)$ $PN$ junction diode is in forward bias, so current will flow the circuit i.e., charge on the capacitor decrease and in time $t$ it becomes $Q = \frac{1}{e}({Q_o})$; where ${Q_o} = CV$
In figure $(i)$ $PN$ junction diode is in forward bias, so current will flow the circuit i.e., charge on the capacitor decrease and in time $t$ it becomes $Q = \frac{1}{e}({Q_o})$; where ${Q_o} = CV$
$ \Rightarrow Q = \frac{{CV}}{e}$
In figure $(ii)$ $P-N$ junction diode is in reverse bias, so no current will flow through the circuit hence change on capacitor will not decay and it remains same i.e. $CV$ after time $t$.
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