Basic Electrical Science (Practice Test)

1) The phase angle difference between current and voltage is 90o, the power will be
A.        minimum
B.         maximum
C.        zero
D.        V.I
                                   
2) If E1 = A.sinωt & E2 = A.sin(ωt - θ), then
A. E1 lags E2 by θ ⁄ 2.
B. E1 leads E2 by θ.
C. E2 leads E1 by θ.
D. E2 leads E1 by θ.
                                   
3) Two sinusoidal quantities are said to be phase quadrature, when their phase difference is
A.        00.
B.         300.
C.        450.
D.        900.
                                   
4) The equation for 25 cycles current sine wave having rms value of 30 amps, will be
A. 42.4sin50πt
B. 30sin50πt
C. 30sin25πt
D. 42.4sin25πt
                                   
5) What will be the rms value of rectangular wave with amplitude 10V
A.        5√2 V
B.         10 V
C.        11.2 V
D.        7.7 V
                                   
6) The current in a circuit follows the law i = 100sinωt. If frequency is 25 Hz how long will it take for the current to rise to 50 Amp ?
A.        1 ms
B.         3.33 ms
C.        10 ms
D.        20 ms
                                   
7)The equation of an emf is given by e = Im[(R2 + 4ω2L2)1/2]sin2ωt. The amplitude of the wave will be
A.        Im[(R2 + 4ω2L2)1/2]
B.         √2Im[(R2 + 4ω2L2)1/2]
C.        [Im(R2 + 4ω2L2)]1/2
D.        2Im[(R2 + 4ω2L2)1/2]
                                   
8) The equation of a current is given by i = Imsin2ωt. The frequency of the current in Hz is
A.        ω ⁄ 2π
B.         ω ⁄ 2
C.        2ω ⁄ π
D.        ω ⁄ π
                                   
9) The RMS value of sinusoidal voltage wave v = 200sinωt, is
A.        100√2 V
B.         200 V
C.        100 V
D.        200√2 V
                                   
10) If one cycle of ac waveform occurs every milli - second, the frequency will be
A.        100 Hz
B.         1000 Hz
C.        50 Hz
D.        10 kHz
                                   
11) If emf in a given circuit is given by e = 100sin628t, then maximum value of voltage and frequency will be
A.        100 V, 100 Hz
B.         100 V, 50 Hz
C.        100√2 V, 100 Hz
D.        50√2 V, 100 Hz
                                   
12) The equation of alternating current is i = 42.4sin628t. Then the average value of current is

A.        42.42 A
B.         38 A
C.        27 A
D.        22 A
                                   
13) A capacitor
A.        passes ac but blocks dc.
B.         passes dc but blocks ac.
C.        passes both ac and dc.
D.        blocks both ac and dc.
                                   
14) The unit of inductive susceptance is
A.        Henry.
B.         Siemens
C.        Ohm
D.        Mho
                                   
15)An inductor supplied with 100V with a frequency of 10 kHz and passes a current of 15.92 mA. The value of inductance is
A.        100 mH
B.         1 H
C.        10 H
D.        100 H.
                                   
16) A 100 μF capacitor supplied from 3V source with a frequency of 50 Hz. The capacitive reactance is
A.        63.68 Ω
B.         31.84 Ω
C.        15.92 Ω
D.        7.96 Ω

Answers
1. c      2. b      3. d      4. a      5. b      6. b      7. a      8. d      9. a      10. b    11. a    12. b    13. a    14. b    15. a    16. c  

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