$A$ student connects a long air-cored coil of manganin wire to a $100 \ V$ $DC$ supply and records a current of $25 \ A$. When the same coil is connected across a $100 \ V, 50 \ Hz$ $AC$ supply,the current reduces to $20 \ A$. The reactance of the coil is $...... \Omega$.

For the $L-R$ circuit shown in the figure,calculate the phase angle in degrees if the frequency is $f = 100/\pi \ Hz$. The inductance is $L = 0.025 \ H$ and the resistance is $R = 5 \ \Omega$.

In the given circuit, the r.m.s. value of the current through the resistor $R$ is:

An arc lamp requires a direct current of $10\ A$ at $80\ V$ to function. If it is connected to a $220\ V$ (rms),$50\ Hz$ $AC$ supply,the series inductor needed for it to work is close to: (in $H$)

An $AC$ source of angular frequency $\omega$ is connected across a resistor $R$ and a capacitor $C$ in series. The current registered is $I$. If the frequency of the source is changed to $\omega/3$ (maintaining the same voltage),the current in the circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency $\omega$.

When an inductance $L$ and resistor $R$ are connected in series to $25 \ V$, $50 \ Hz$ supply, a current of $0.5 \ A$ flows in the circuit. The current lags behind in phase from applied voltage by $(\frac{\pi}{3})$ radian. The value of $R$ is $(\cos 60^{\circ} = \frac{1}{2})$ (in $\Omega$)