In the circuit shown,the power factor of the circuit is $1$ and the power factor of the box is $\frac{3}{5}$. Find the reading of the ammeter in $A$.

$A$ series $LCR$ circuit is connected to an ac source of $220\,V, 50\,Hz$. The circuit contains a resistance $R=100\,\Omega$ and an inductor of inductive reactance $X_L=79.6\,\Omega$. The capacitance of the capacitor needed to maximize the average rate at which energy is supplied will be $..........\mu F$.

In the given circuit,the voltmeter reads $75 \ V$. The value of $C$ is $.... \mu F$. (Given: $\pi^2 = 10$)

Match List-$I$ with List-$II$ :

List-$I$	List-$II$
$(a)$ $\omega L > \frac{1}{\omega C}$	$(i)$ Current is in phase with $emf$
$(b)$ $\omega L = \frac{1}{\omega C}$	$(ii)$ Current lags behind the applied $emf$
$(c)$ $\omega L < \frac{1}{\omega C}$	$(iii)$ Maximum current occurs
$(d)$ Resonant frequency	$(iv)$ Current leads the $emf$

Choose the correct answer from the options given below :

An $LC$ series resonant circuit produces a resonant frequency $f$. If $L$ is tripled and $C$ is increased by $3C$ (making the new capacitance $4C$),the new resonant frequency will be:

In a series $LR$ circuit with $X_L = R$, the power factor is $P_1$. If a capacitor of capacitance $C$ with $X_C = X_L$ is added to the circuit, the power factor becomes $P_2$. The ratio of $P_1$ to $P_2$ will be: