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Alternating Current

116 Questions Start Allen Test
All Exams Allen
Q26 Allen SIMPLE AC CIRCUIT MCQ
A capacitor of capacity C is connected in A.C. circuit. The applied emf is $V=V_{0}\sin\omega t$ , then the current is:
A.
$I = \frac{V_{0}}{\omega L} \sin \omega t$
B.
$I = \frac{V_{0}}{\omega L} \sin (\omega t + \pi/2)$
C.
$I = V_{0} \omega C \sin \omega t$
D.
$I = V_{0} \omega C \sin (\omega t + \pi/2)$
Q27 Allen SIMPLE AC CIRCUIT MCQ
The impedance of a circuit, when a resistance R and an inductor of inductance L are connected in series in an A.C. circuit of frequency (f) is:
A.
$\sqrt{R + 4\pi fL^2}$
B.
$\sqrt{R + 4\pi^2f^2L^2}$
C.
$\sqrt{R^2 + 4\pi^2f^2L^2}$
D.
$\sqrt{R^2 + 2\pi^2f^2L^2}$
Q28 Allen SIMPLE AC CIRCUIT MCQ
A capacitor of capacity C and reactance X if capacitance and frequency become double then reactance will be :-
A.
4X
B.
$\frac{\mathrm{X}}{2}$
C.
$\frac{\mathrm{X}}{4}$
D.
2X
Q29 Allen SIMPLE AC CIRCUIT MCQ
The coil of choke in a circuit:
A.
increases the current
B.
controls the current
C.
has high resistance to d.c. circuit
D.
does not change the current
Q30 Allen SIMPLE AC CIRCUIT MCQ
The inductive reactance of an inductive coil with $\frac{1}{\pi}$ henry and $50\mathrm{Hz}:$ -
A.
$\frac{50}{\pi}$ ohm
B.
$\frac{\pi}{50}$ ohm
C.
100 ohm
D.
50 ohm
Q31 Allen SIMPLE AC CIRCUIT MCQ
In the L-R circuit R = 10Ω and L = 2H. If 120V, 60Hz alternating voltage is applied then the flowing current in this circuit will be :
A.
0.32 A
B.
0.16 A
C.
0.48 A
D.
0.80 A
Q32 Allen SIMPLE AC CIRCUIT MCQ
An inductance of 0.4 Henry and a resistance of 100 ohm are connected to a A.C. voltage source of 220 V and 50 Hz. Then find out the phase difference between the voltage and current flowing in the circuit:
A.
$\tan^{-1}(2.25\pi)$
B.
$\tan^{-1}(0.4\pi)$
C.
$\tan^{-1}(1.5\pi)$
D.
$\tan^{-1}(0.5\pi)$
Q33 Allen SIMPLE AC CIRCUIT MCQ
A capacitor of capacitance $100 \mu F$ & a resistance of $100\Omega$ is connected in series with AC supply of 220V, 50Hz. The current leads the voltage by
A.
$\tan^{-1}\left(\frac{1}{2\pi}\right)$
B.
$\tan^{-1}\left(\frac{1}{\pi}\right)$
C.
$\tan^{-1}\left(\frac{2}{\pi}\right)$
D.
$\tan^{-1}\left(\frac{4}{\pi}\right)$
Q34 Allen SIMPLE AC CIRCUIT MCQ
If the current through an inductor of inductance L is given by $I = I_{0} \sin \omega t$ , then the voltage across inductor will be :-
A.
$I_{0} \omega L \sin (\omega t - \pi/2)$
B.
$I_{0} \omega L \sin (\omega t + \pi/2)$
C.
$I_{0} \omega L \sin (\omega t - \pi)$
D.
None of these
Q35 Allen SIMPLE AC CIRCUIT MCQ
There is a 5 Ω resistance in an A.C. circuit. Inductance of 0.1 H is connected with it in series. If equation of A.C. e.m.f. is V = 5 sin50t then the phase difference between current and e.m.f. is :-
A.
$\frac{\pi}{2}$
B.
$\frac{\pi}{6}$
C.
$\frac{\pi}{4}$
D.
0
Q36 Allen SIMPLE AC CIRCUIT MCQ
A 50 Hz a.c. source of 20V is connected across R and C as shown in figure below. The voltage across R is 12V. The voltage across C is
A.
8 V
B.
16V
C.
10 V
D.
Not possible to determine unless values of R and C are given
Q37 Allen SIMPLE AC CIRCUIT MCQ
200Ω resistance and 1H inductance is connected in series with an A.C. circuit. The frequency of the source is $\frac{200}{2\pi}$ Hz. Then phase difference in between V and I will be:
A.
30°
B.
60°
C.
45°
D.
90°
Q38 Allen SIMPLE AC CIRCUIT MCQ
Impedance of the following circuit will be :
A.
$150\Omega$
B.
$200\Omega$
C.
$250\Omega$
D.
$340\Omega$
Q39 Allen SIMPLE AC CIRCUIT MCQ
In the figure shown, find $V_{R}$ :
A.
132V
B.
396V
C.
185 V
D.
$\sqrt{220 \times 176}\mathrm{V}$
Q40 Allen SIMPLE AC CIRCUIT MCQ
If alternating current of 60 Hz frequency is flowing through inductance of L = 1 mH and drop in $\Delta V_{L}$ is 0.6 V then alternating current:
A.
$\frac{1}{\pi} A$
B.
$\frac{5}{\pi} A$
C.
$\frac{50}{\pi} A$
D.
$\frac{20}{\pi} A$
Q41 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
An inductance of 1mH, a condenser of $10\mu F$ and a resistance of $50\Omega$ are connected in series. The reactance of inductor and condensers are same. The reactance of either of them will be :-
A.
$100\ \Omega$
B.
$30\ \Omega$
C.
$3.2\ \Omega$
D.
$10\ \Omega$
Q42 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
L, C and R represent physical quantities inductance, capacitance and resistance respectively. The combination representing dimension of frequency is
A.
LC
B.
$(\mathrm{LC})^{-1/2}$
C.
$\left(\frac{\mathrm{L}}{\mathrm{C}}\right)^{-1/2}$
D.
$\frac{C}{L}$
Q43 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
A circuit contains R, L and C connected in series with an A. C. source. The values of the reactance for inductor and capacitor are $200\Omega$ and $600\Omega$ respectively and the impedance of the circuit is $Z_{1}$ . What happens to the impedance of the same circuit if the values of the reactance are interchanged:-
A.
The impedance will remain unchanged
B.
The impedance will increase
C.
The impedance will decrease
D.
Information insufficient
Q44 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
When V = 100 sinωt is applied across a series (R-L-C) circuit, at resonance the current in resistance (R = 100 Ω) is i = i₀ sinωt, then power dissipation in circuit is:-
A.
50 W
B.
100 W
C.
25 W
D.
Can't be calculated
Q45 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
At resonance in a series LCR circuit, which of the following statements is true: -
A.
Current in the circuit is maximum and phase difference between E and I is $\pi/2$
B.
Current in the circuit is maximum and phase difference between E and I is zero
C.
Voltage is maximum and phase difference between E and I is $\pi/2$
D.
Current is minimum and phase difference between E and I is zero
Q46 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
An alternating voltage is connected in series with a resistance R and an inductance L. If the potential drop across the resistance is 200 volt and across the inductance is 150 volt, the applied voltage:
A.
350 volt
B.
250 volt
C.
500 volt
D.
300 volt
Q47 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
For a series R-L-C circuit :-
(a) Voltage across L and C are differ by $\pi$ (b) Current through L and R are in same phase
(c) Voltage across R and L differ by $\pi/2$ (d) Voltage across L and current through C are differ by $\pi/2$
A.
a, b, c
B.
b, c, d
C.
c, d, a
D.
All
Q48 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
A series R-L-C (R = 10Ω, X $_{L}$ = 20Ω, X $_{C}$ = 20 Ω) circuit is supplied by V = 10 sin ωt volt then power dissipation in circuit is :-
A.
Zero
B.
10 W
C.
5 W
D.
2.5 W
Q49 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
The self inductance of the motor of an electric fan is 10 H. In order to impart maximum power at 50 Hz. It should be connected to a capacitance of:
A.
$2 \times 10^{-6}$ F
B.
$3 \times 10^{-6}$ F
C.
$10^{-4}$ F
D.
$10^{-6}$ F
Q50 Allen LCR SERIES CIRCUIT, RESONANCE MCQ
In a series resonant R-L-C circuit, if L is increased by 25% and C is decreased by 20%, then the resonant frequency will :
A.
Increases by 10%
B.
Decreases by 10%
C.
Remain unchanged
D.
Increases by 2.5%