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11
MCQ (Multiple Correct Answer)

For a $L-C-R$ circuit, the power transferred from the driving source to the driven oscillator is $P=I^2 Z \cos \phi$.

A
Here, the power factor $\cos \phi \geq 0, P \geq 0$
B
The driving force can give no energy to the oscillator $(P=0)$ in some cases
C
The driving force cannot syphon out $(P<0)$ the energy out of oscillator
D
The driving force can take away energy out of the oscillator
12
MCQ (Multiple Correct Answer)

When an $A C$ voltage of 220 V is applied to the capacitor $C$

A
the maximum voltage between plates is 220 V
B
the current is in phase with the applied voltage
C
the charge on the plates is in phase with the applied voltage
D
power delivered to the capacitor is zero
13
MCQ (Multiple Correct Answer)

The line that draws power supply to your house from street has

A
zero average current
B
220 V average voltage
C
voltage and current out of phase by $90 \Upsilon$
D
voltage and current possibly differing in phase $\phi$ such that $|\phi|<\frac{\pi}{2}$
14
Subjective

If a L-C circuit is considered analogous to a harmonically oscillating springblock system, which energy of the L-C circuit would be analogous to potential energy and which one analogous to kinetic energy?

Explanation

If we consider a L-C circuit analogous to a harmonically oscillating springblock system. The electrostatic energy $\frac{1}{2} C V^2$ is analogous to potential energy and energy associated with moving charges (current) that is magnetic energy $\left(\frac{1}{2} L I^2\right)$ is analogous to kinetic energy.

15
Subjective

Draw the effective equivalent circuit of the circuit shown in figure, at very high frequencies and find the effective impedance.

Explanation

We know that inductive reactance $X_L=2 \pi f L$

and capacitive reactance $X_C=\frac{1}{2 \pi f C}$

For very high frequencies $(f \rightarrow \infty), X_L \rightarrow \infty$ and $X_C \rightarrow 0$

When reactance of a circuit is infinite it will be considered as open circuit. When reactance of a circuit is zero it will be considered as short circuited.

So, $C_1, C_2 \rightarrow$ shorted and $L_1, L_2 \rightarrow$ opened.

So, effective impedance $=R_{\text {eq }}=R_1+R_3$