Time Constant

Q. What is the time constant of a circuit where a pacitor(C=10nF) is being charged connected to a cell through a resistor of $10\Omega$?

1. 100ns
2. 1ns
3. 10ns
4. 1us

Q. A series $R-C$ combination is connected to an ac voltage of angular frequency $\omega =500rad/s$. If the impedance of the R-C circuit is $R\sqrt{1.25}$, the time constant (in millisecond) of the circuit is

Q. A capacitor discharges through a resistance. The stored energy $U_0$ in one capacitive time constant falls to

1. $\frac{U_0}{e^2}$
2. $e{U}_0$
3. $\frac{U_0}{e}$
4. None of these

Q. The time constant of a capacitor is 5sec. If the capacitance is C=100nF and it is charged from zero by a cell of EMF 10V through a resistor. What is the charge on it after 3 seconds?

1. $4\times {10}^{-7}C$
2. $4.5\times {10}^{-7}C$
3. $5\times {10}^{-7}C$
4. $5.5\times {10}^{-7}C$