A resistance of $400\,\Omega$ is connected in series with an inductor of $(3 / \pi)$ $H$ and this combination is connected across an $A.C.$ source as shown in figure.

When a coil is connected across a $20 \mathrm{~V}$ dc supply, it draws a current of $5 \mathrm{~A}$. When it is connected across $20 \mathrm{~V}, 50 \mathrm{~Hz}$ ac supply, it draws a current of $4 \mathrm{~A}$. The self inductance of the coil is ………….. $\mathrm{mH}$. (Take $\pi=3$ )

Frequency of $L-C$ circuit is $f_{1} .$ If a resistance $R$ is also added to
it, the frequency becomes $f_{2}$. The ratio of $\frac{f_{2}}{f_{1}}$ will be

A bulb and a capacitor are connected in series to a source of alternating current. If its frequency is increased, while keeping the voltage of the source constant, then

A $12\,\Omega $ resistor and a $0.21\, H$ inductor are connected in series to an $ac$ source operating at $20 \,volts$, $50\,cycle/second$. The phase angle between the current and the source voltage is…..$^o$