$$\begin{gathered} 1. \varphi = 0 \\ 2. 0\le \varphi <\frac{\mathrm{\pi }}{2} \\ 3.\frac{\mathrm{\pi }}{2}<\varphi <\mathrm{\pi } \\ 4. \varphi =\mathrm{\pi } \end{gathered}$$

A: On the increasing frequency of a.c. through a conductor resistance of the circuit may increase.

R: Resistance of a conductor is directly proportional to the frequency of the a.c. input

The primary and secondary coils of an ideal transformer have 100 and 5000 turns respectively. The magnetic flux linking the primary coil is given by $\varphi$= 20t + 10. The output voltage across the secondary coil is

In the LCR-circuit shown below, if the reading of the voltmeters $V_{1 }$and $V_2$ are same, then

If R and L are resistance and inductance of a choke coil and f is the frequency of current through it, then the average power of the choke coil is proportional to:

Which of the following is/are copper loss/losses in a transformer?

Half power frequencies for the circuit shown below are 200rad/s and 800 rad/s. The value of the product LC is $(is secon{d}^2/radia{n}^2)$

$$\begin{gathered} 1. 6.25 \times {10}^{-3} \\ 2. 6.25\times {10}^{-6} \\ 3. 1.25\times {10}^{-3} \\ 4. 1.25\times {10}^{-5} \end{gathered}$$

What is the reading of the a.c. voltmeter in the network shown below?
                  

The power factor of the given circuit is
           
$$\begin{gathered} 1. \frac{1}{2} \\ 2. \frac{1}{\sqrt{2}} \\ 3. \frac{\sqrt{3}}{2} \\ 4. 0 \end{gathered}$$

In LC oscillation, the current in the circuit when the total energy is stored in the form of magnetic energy is- $(where q_0 is maximum charge stored by capacitor)$

$$\begin{gathered} 1. Zero \\ 2. \frac{q_0}{\sqrt{Lc }} \\ 3. \frac{q_0}{LC } \\ 4. q_0\sqrt{LC} \end{gathered}$$

The variation of alternating current (l) with time (t) is shown in the given graph. Find the average value of current for half cycle

$$\begin{gathered} 1. \frac{2{/}_0}{\pi } \\ 2. \frac{l_0}{\sqrt{2}} \\ 3. \frac{l_0}{2} \\ 4. Zero \end{gathered}$$

A capacitor and a resistor are connected in series across a.c. supply. Which of the following phasor diagram may be correct?

An inductor of inductance (L), a capacitor of capacitance (C), and a resistor of resistance (R) are connected in series across $E=E_0\sin \frac{t}{\sqrt{LC}}$, The reading of hot wire voltmeter connected across the resistor is

$$\begin{gathered} 1. E_0 \\ 2. \frac{E_0}{\sqrt{2}} \\ 3. \frac{E_0}{2} \\ 4. zero \end{gathered}$$

The power factor of a series LCR circuit in resonance condition is:

$$\begin{gathered} 1. zero \\ 2. \frac{1}{2} \\ 3. \frac{1}{\sqrt{2}} \\ 4. 1 \end{gathered}$$

A: In an LCR circuit, the total energy stored is constant at resonance.

R: Resistance of the LCR circuit doesn't affect the total energy stored in the circuit at resonance.

A: Average value of AC is always zero in a one-time period.

R: Net charge transferred in one time period of AC is zero

The instanteneous power of resistor having resistance R across ac supply of $E=E_{0 }\sin \omega t$ is

$$\begin{gathered} 1. \frac{{E_0}^2}{R}{\sin }^2 \omega t \\ 2. \frac{{E_0}^2}{R}{\cos }^2 \omega t \\ 3. \frac{{E_0}^2}{R} \\ 4. zero \end{gathered}$$

The ratio of resonant angular frequency and bandwidth of a given series LCR circuit is-

An electric bulb rated 100 W, 40 V has to be operated across 50 V, 50 Hz a.c supply. The capacitance of the capacitor which has to be connected in series will the bulb is

$$\begin{gathered} 1. 12 F \\ 2. 24\pi F \\ 3. \frac{6}{\pi }F \\ 4. \frac{1}{1200\pi }F \end{gathered}$$

An electricbulb is connected in series with an inductor across a.c supply. When an iron is inserted in the inductor, the brightness of bulb

The quality factor of the series resonant circuit is

$$\begin{gathered} 1. 2\pi x\frac{Maximum energy stored }{Energy dissipation per cycle } \\ 2. \frac{Resonant frequency }{Band width } \\ 3. \frac{Potential difference across capacitor }{Potential difference across resistor } \\ 4. All of these \end{gathered}$$

When alternating current flows through a conductor, the rate of flux change

In a step-up transformer, the turn ratio is 1: 20. The resistance of 100 $\Omega$ connected across the secondary is drawing a current of 2A. The primary voltage and the current respectively are

An ideal inductor of 20 H is joined in series with a resistance of 5 ohms and a battery of 5V. The current flowing in the circuit after 4s is ( in amperes)

$$\begin{gathered} 1. \frac{1}{e} \\ 2. e \\ 3. 1-\frac{1}{e } \\ 4. 1-e \end{gathered}$$

The RMS value of the current in a series LCR circuit is plotted with angular frequency as shown below. The ohmic resistance is R, inductance is L and capacitance is C in the circuit. The value of the difference (${\omega }_2-{\omega }_1)$is

$$\begin{gathered} 1. \frac{R}{L} \\ 2. \frac{L}{R} \\ 3. \frac{1}{\sqrt{LC}} \\ 4. \frac{1}{\sqrt{2LC}} \end{gathered}$$

In the circuit diagram shown below, the reading of the a.c. voltmeter is

In a series RLC alternating current circuit, the r.m.s. value of current is $l$, the average power loss in the circuit is

$$\begin{gathered} 1. l^2 R \\ 2. l^2 \omega L \\ 3. l^{2 }\omega C \\ 4. l^2 \left(\omega L-\frac{1}{\omega C}\right) \end{gathered}$$

A step-down transformer transforms 200 V to 100 volts. If the current in primary and secondary coils are 6 A and 9.6 A respectively, the efficiency of the transformer is

It is found that current through the LCR series circuit is maximum. If $V_r ,V_c and V_L$ are potential differences across resistance, capacitor, and inductor respectively, then which of the following is correct?

$$\begin{gathered} 1. V_r =V_L > V_C \\ 2. V_R \ne V_L = V_C \\ 3. V_R \ne V_L \ne V_C \\ 4. V_{R }= V_C \ne V_L \end{gathered}$$

An ideal inductor connected to a cell is shown in figure. Select the correct relations between readings of ammeters $A_1 and A_2$ just after the switch is closed and a long time after closing the switch

$$\begin{gathered} 1. A_1>A_2 ; A_1<A_2 \\ 2. A_1>A_{2 }; A_2=A_1 \\ 3. A_1<A_2 ; A_1 < A_2 \\ 4. A_1<A_2 ; A_1 =A_2 \end{gathered}$$