SSC Junior Engineer Electrical Online Exam 2018 CPWD/CWC/MES Electrical Engineering 22-01-2018 Morning4

31. Determine the root means square value (in V) of the voltage waveform given in the figure below?

A) 56.56
B) 46.52
C) 32.25
D) 28.29

... Answer is D)
This sinusoidal wave and RMS value for sinusoidal wave = Vm / √2 = 0.707 *Vm Vm = 40 Volt V Rms = .707 * 40 = 28.29 V .

32. Determine the time-period (in ms) of a sinusoidal wave when the frequency of the wave is 60 Hz?

A) 16.67
B) 18.26
C) 20.24
D) 26

... Answer is A)
frequency = 60 Hz
Time-period = 1/frequency
Time-period = 1/60 = 0.01667 second = 16.67 mili second
.

33. Which of the following is the unit of frequency of an AC signal?

A) Hertz/Second
B) Revolution
C) Hertz
D) Revolution/second

... Answer is C)
Hertz is the unit of frequency of an AC signal.

34. Which one of the following is the CORRECT relation between the peak value and RMS value of current for a sine wave?

A) Irms = 0.06 Ip
B) rms = 0.87 Ip
C) Irms = 1.414 Ip
D) Irms = 0.707 Ip

... Answer is D)
RMS value of current for a sine wave
= Ip / √2
= Ip/1.414 = .707 Ip
.

35. Determine the average value of alternating voltage (in V) when the peak value of the voltage is 120 V?

A) 76.44
B) 86.34
C) 110.34
D) 188.38

... Answer is A)
peak value of the voltage Vm = 120 V
Avarage value of volage is = 2Vm/p = .637 * Vm
= .637*120 = 76.44 V
.

36. What will be the capacitance (in mF) of a circuit is supplied with a 50 Hz frequency and the capacitive reactance of the circuit is 40 ohms?

A) 0.4
B) 0.8
C) 1.4
D) 2.6

... Answer is )
capacitive reactance Xc = 40 ohm

capacitive reactance Xc =1/ 2*p*f*c

c = 1/2*p*f*Xc = 1 /2*3.14*50*40

= 1/314*40 F = 1000/314*40 mF = 0.08 mF
ALL are worng Answer .

37. Determine the total power (in kW) consumed by a 3-phase delta connected system supplied by a line voltage of 240 V when the value of phase current is 20 A and the current lags the voltage by 60 degree. 240?

A) 9.4
B) 8.6
C) 8.2
D) 7.2

... Answer is D)
Power in three phase P= 1.732 *Vl *Il * Cosf

Line voltage Vl=240 v
Line current Il= 1.732 *I phase

P= 1.732 *Vl *Il * Cosf

= 1.732*240*1.732*20 cos 60

=3 *4800 *1/2 = 14400/2 = 7200 watt = 7.2 kw

38. Determine the capacitive susceptence (in Siemens) of a circuit if the capacitor of the circuit is 0.08 mF and supplied with a 50 Hz frequency?

A) 0.025
B) 0.034
C) 0.046
D) 0.064

... Answer is A)
susceptence = 1/reactance
Reactance Xc = 1/2pfc
susceptence = 2pfc = 2 * 3.14 * 50 * 0.08 * $10^-3$
= 0.025 Siemens .

39. What will be the transient time (in seconds) of a series RC circuit when the value of the capacitance is 600 microfarad and the value of the resistance is 20 kilo-ohms?

A) 10
B) 12
C) 14
D) 16

... Answer is B)
transient time (time constant)(t) =R*C second
time constant(t)= 20*$10^3$ * 600*$10^-6$
time constant(t)= 12000*$10^-3$
time constant(t)= 12 second .

40. What will be the resonant (in kHz) of a tank circuit when the capacitance and inductance of the circuit is 0.04 mF and 0.04 mH respectively?

A) 8
B) 6
C) 4
D) 1

... Answer is C)
Resonant frequency = 1/2p LC
capacitance =0.04 mF = 0.04*$10^-3$
inductance =0.04 mH =0.04*$10^-3$
Resonant frequency = 1/2p LC
Resonant frequency = 1/ .





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