$A$ filter circuit used in a rectifier has a load resistance of $200 \Omega$ and a capacitance of $15 \mu\text{F}$. The value of the time constant is . . . . . . .

After the switch shown in Figure $A$ is closed,there is a current $i$ through the resistance $R$. Figure $B$ indicates current variation curves $a, b, c,$ and $d$ for four sets of values of $R$ and capacitance $C$:
$(i)$ $R_0$ and $C_0$
$(ii)$ $2R_0$ and $C_0$
$(iii)$ $R_0$ and $2C_0$
$(iv)$ $2R_0$ and $2C_0$
Which set goes with which curve?

At $t = 0$,switch $S$ is closed. The charge on the capacitor is varying with time $t$ as $Q = Q_0(1 - e^{-\alpha t})$. Find the value of $Q_0$.

$A$ capacitor of capacitance $5\,\mu F$ is connected to a source of constant $emf$ of $200\,V$ for a long time. Then,the switch is shifted from contact $1$ to contact $2$. The total amount of heat generated in the $500\,\Omega$ resistance thereafter is: (in $/32\,J$)

$A$ $4 \mu F$ capacitor and a resistance of $2.5 \, M\Omega$ are in series with a $12 \, V$ battery. Find the time after which the potential difference across the capacitor is $3$ times the potential difference across the resistor. (Given $\ln(2) = 0.693$)

The charge across the capacitor in two different $RC$ circuits $1$ and $2$ are plotted as shown in the figure. Choose the correct statement$(s)$ related to the two circuits.