Physics - Alternating Current - Quiz-2

In the circuit shown below, the ac source has voltage $V = 20 \cos (ω t)$ volts with ω = 2000 rad/sec. the amplitude of the current will be nearest to

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2 A
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3.3 A
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$2 / \sqrt{5} A$
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$\sqrt{5} A$

In an ac circuit the reactance of a coil is $\sqrt{3}$ times its resistance, the phase difference between the voltage across the coil to the current through the coil will be

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π/3
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π/2
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π/4
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π/6

The power factor of an ac circuit having resistance (R) and inductance (L) connected in series and an angular velocity ω is

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$R / ω L$
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$R / {(R^{2} + ω^{2} L^{2})}^{1 / 2}$
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$ω L / R$
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$R / {(R^{2} - ω^{2} L^{2})}^{1 / 2}$

An inductor of inductance L and resistor of resistance R are joined in series and connected by a source of frequency ω. The power dissipated in the circuit is :

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$\frac{(R^{2} + ω^{2} L^{2})}{V}$
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$\frac{V^{2} R}{(R^{2} + ω^{2} L^{2})}$
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$\frac{V}{(R^{2} + ω^{2} L^{2})}$
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$\frac{\sqrt{R^{2} + ω^{2} L^{2}}}{V^{2}}$

In an LCR circuit, the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30V and that between the terminals of resistance is 40V. The supply voltage will be equal to:

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50 V
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70 V
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130 V
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10 V

In a circuit L, C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45°. The value of C is

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$\frac{1}{2 π f (2 π f L + R)}$
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$\frac{1}{π f (2 π f L + R)}$
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$\frac{1}{2 π f (2 π f L - R)}$
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$\frac{1}{π f (2 π f L - R)}$

In an LR-circuit, the inductive reactance is equal to the resistance R of the circuit. An e.m.f. $E = E_{0} \cos (ω t)$ applied to the circuit. The power consumed in the circuit is:

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$\frac{E_{0}^{2}}{R}$
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$\frac{E_{0}^{2}}{2 R}$
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$\frac{E_{0}^{2}}{4 R}$
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$\frac{E_{0}^{2}}{8 R}$

One 10 V, 60 W bulb is to be connected to 100 V line. The required induction coil has a self-inductance of value: (f = 50 Hz)

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0.052 H
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2.42 H
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16.2 mH
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1.62 mH

In the circuit given below, what will be the reading of the voltmeter

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300 V
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900 V
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200 V
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400 V

In the circuit shown below, what will be the readings of the voltmeter and ammeter?

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800 V, 2 A
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300 V, 2 A
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220 V, 2.2 A
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100 V, 2 A

The diagram shows a capacitor C and a resistor R connected in series to an ac source. V₁ and V₂ are voltmeters and A is an ammeter:

Consider now the following statements

I. Readings in A and V₂ are always in phase

II. Reading in V₁ is ahead in phase with reading in V₂

III. Readings in A and V₁ are always in phase

Which of these statements is/are correct?

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I only
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II only
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I and II only
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II and III only

In the circuit shown in figure neglecting source resistance the voltmeter and ammeter reading will respectively, will be

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0V, 3A
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150V, 3A
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150V, 6A
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0V, 8A

In the circuit shown in the figure, the ac source gives a voltage $V = 20 \cos (2000 t) .$ Neglecting source resistance, the voltmeter and ammeter reading will be:

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0V, 0.47A
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1.68V, 0.47A
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0V, 1.4 A
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5.6V, 1.4 A

An ac source of angular frequency ω is fed across a resistor r and a capacitor C in series. The current registered is I. If now the frequency of the source is changed to ω/3 (but 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 ω.

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$\sqrt{\frac{3}{5}}$
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$\sqrt{\frac{2}{5}}$
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$\sqrt{\frac{1}{5}}$
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$\sqrt{\frac{4}{5}}$

For a series RLC circuit R = X_L = 2X_C. The impedance of the circuit and phase difference between V and i will be:

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$\frac{\sqrt{5} R}{2}, \tan^{- 1} (2)$
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$\frac{\sqrt{5} R}{2}, \tan^{- 1} (\frac{1}{2})$
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$\sqrt{5} X_{C}, \tan^{- 1} (2)$
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$\sqrt{5} R, \tan^{- 1} (\frac{1}{2})$

In the adjoining ac circuit the voltmeter whose reading will be zero at resonance is

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V₁
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V₂
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V₃
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V₄

In the adjoining figure, the impedance of the circuit will be:

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120 ohm
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50 ohm
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60 ohm
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90 ohm

Which one of the following curves represents the variation of impedance (Z) with frequency (f) in a series LCR circuit?

1.		2.
3.		4.

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1
0%
2
0%
3
0%
4

The variation of the instantaneous current (I) and the instantaneous emf (E) in a circuit are shown in the figure. Which of the following statements is correct?

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The voltage lags behind the current by π/2.
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The voltage leads the current by π/2.
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The voltage and the current are in phase.
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The voltage leads the current by π.

The figure shows the variation of R, X_L, and X_C with frequency f in a series L, C, R circuit. Then for what frequency point, the circuit is inductive:

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A
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B
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C
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All points

An ac source of variable frequency f is connected to an LCR series circuit. Which one of the graphs in the figure represents the variation of the current I in the circuit with frequency f :

A constant voltage at different frequencies is applied across a capacitance C as shown in the figure.

Which of the following graphs correctly depicts the variation of current with frequency?

1.		2.
3.		4.

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1
0%
2
0%
3
0%
4

The output current versus time curve of a rectifier is shown in the figure. The average value of output current in this case is

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0
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$\frac{I_{0}}{2}$
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$\frac{2 I_{0}}{π}$
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I₀

The current 'i' in an inductance coil varies with time 't' according to the following graph.

Which one of the following plots shows the variations of voltage in the coil?

When an ac source of e.m.f. $e = E_{0} \sin (100 t)$ is connected across a circuit, and the phase difference between the e.m.f. e and the current i in the circuit is observed to be $\frac{\pi}{4}$ as shown in the diagram. If the circuit consists possibly only of RC or LC in series, then the relationship between the two elements is given by:

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$R = 1 k Ω, C = 10 μ F$
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$R = 1 k Ω, C = 1 μ F$
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$R = 1 k Ω, L = 10 H$
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$R = 1 k Ω, L = 1 H$

Two sinusoidal voltages of the same frequency are shown in the diagram. What is the frequency, and the phase relationship between the voltages?

	Frequency in Hz	Phase lead of N over M in radians
1.	0.4	–π/4
2.	2.5	–π/2
3.	2.5	+π/2
4.	2.5	–π/4

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1
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2
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3
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4

Which of the following plots may represent the reactance of a series LC combination?

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a
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b
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c
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d

Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication?

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(a) $R = 20 Ω, L = 1.5 H, C = 35 μ F$
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(b) $R = 25 Ω, L = 2.5 H, C = 45 μ F$
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(c) $R = 15 Ω, L = 3.5 H, C = 30 μ F$
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(d) $R = 25 Ω, L = 1.5 H, C = 45 μ F$

The potential differences across the resistance, capacitance and inductance are 80V, 40Vand 100V respectively in an L-C-R circuit. The power factor of this circuit is

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0.4
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0.5
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0.8
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1.0

A 100 $Ω$ resistance and a capacitor of 100 $Ω$ reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is

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2.2 A
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11A
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4.4A
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11 $\sqrt{2}$ A

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Practice Physics Quiz Questions and Answers

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Practice Physics Quiz Questions and Answers

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