50 Most Important Basic Electrical Objective Type Question with solution| MCQ Of Basic Electrical with explanation
Ques 1. A sine wave has a frequency of 50 Hz. Its angular frequency is _______radian/second.
100 π
50 π
25 π
5 π
Answer.1. 100 π
Explanation:
The relation between angular velocity and frequency is given as
ω = 2πf rad/sec
ω = 2xπx50
= 100π
Ques 2. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.
5
5
10
15
Answer.3. 10
Explanation:
Capacitive reactance
Xc = 1/2πf
Therefore XC1/XC2 = 2πf2/2πf1
= 20/XC2 =100/50
= XC2 = 10
Ques 3. The period of a wave is
The same as frequency
Time required to complete one cycle
Expressed in amperes
None of the above
Answer.3. Time required to complete one cycle
Explanation:
The period of a wave is the time for a particle on a medium to make one complete vibrational cycle.
Ques 4. The form factor is the ratio of
Peak value to r.m.s. value
r.m.s. value to average value
Average value to r.m.s. value
None of the above
Answer.2. r.m.s value to average value
Explanation:
The form factor of an alternating current waveform (signal) is the ratio of the RMS (root mean square) value to the average value (mathematical mean of absolute values of all points on the waveform).
Ques 5. The period of a sine wave is 0.02 seconds. Its frequency is
20 Hz
30 Hz
40 Hz
50 Hz
Answer.4. 50 Hz
Explanation:
Frequency = 1/period
= 1/0.02
= 50 Hz
Ques 6. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to
Average voltage
R.M.S voltage
Peak voltage
None of the above
Answer.2. R.M.S voltage
Explanation:
In AC system, we can’t take average value because average value is equal to zero over a period in AC.
So now to calculate different parameters like voltage, current, etc we need RMS value. This is the reason why we use RMS quantities while dealing with AC.
Ques 7. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is
A sinusoid of the same frequency
A sinusoid of half the original frequency
A sinusoid of double the frequency
Not a sinusoid
Answer.1. A sinusoid of the same frequency
Explanation:
Adding two sinusoids of the same frequency but with possibly different amplitudes and phases, produces another sinusoid at that frequency.
When alternating waveforms have the same frequency but different phase, they are said to be “Out of phase”.
The equation of A.C sin wave is given as:
Vst = Asin(ω x t)
Vst = Asin(2πft)
Where Vs is the A.C signal voltage with the peak amplitude of “A” volts
Let us take an example
Suppose we add the two sinusoidal with amplitude of A and B but having the same frequencies the equation can be written as
Vt = V1t + V2t
= Asin(ω x t) + Bsin(ω x t)
= (A +B) sin(ω x t)
Hence the amplitude is added up but the frequency remains same.
Ques 8. The peak value of a sine wave is 200 V. Its average value is
127.4 V
141.4 V
282.8 V
200V
Answer.1. 127. 4 V
Explanation:
For sinusoidal waveform
Peak Factor = peak value/R.M.S value = 141.44
Hence R.M.S value = 200/1.414 = 141.44
Form factor = R.M.S value/ Average value
Hence average value = 141.44/1.11
=127.42 V
Ques 9 If two sine waves of the same frequency have a phase difference of π radians, then
Both will reach their minimum values at the same instant
Both will reach their maximum values at the same instant
When one wave reaches its maximum value, the other will reach its minimum value
None of the above
Answer.3. When one wave reaches its maximum value, the other will reach its minimum value
Explanation: If the phase difference is 180 degrees (π radians), then the two sine waves are said to be in antiphase or Phase opposition i.e if one wave reaches its maximum value, then other will reach its minimum value.
Ques 10. The voltage of domestic supply is 230V. This figure represents
Mean value
R.M.S value
Peak value
Average value
Answer.2. R.M.S value
Explanation: Root Mean Square is the actual value of an alternating quantity which tells us an energy transfer capability of an AC source. The domestic single phase AC supply is 230 V, 50 hertz, where 230 V is the R.M.S value of alternating voltage