# 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.

1. 100 π
2. 50 π
3. 25 π
4. 5 π

Explanation:

The relation between angular velocity and frequency is given as

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.

1. 5
2. 5
3. 10
4. 15

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

1. The same as frequency
2. Time required to complete one cycle
3. Expressed in amperes
4. 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

1. Peak value to r.m.s. value
2. r.m.s. value to average value
3. Average value to r.m.s. value
4. 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

1. 20 Hz
2. 30 Hz
3. 40 Hz
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

1. Average voltage
2. R.M.S voltage
3. Peak voltage
4. None of the above

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

1. A sinusoid of the same frequency
2. A sinusoid of half the original frequency
3. A sinusoid of double the frequency
4. 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

1. 127.4 V
2. 141.4 V
3. 282.8 V
4. 200V

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

1. Both will reach their minimum values at the same instant
2. Both will reach their maximum values at the same instant
3. When one wave reaches its maximum value, the other will reach its minimum value
4. 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

1. Mean value
2. R.M.S value
3. Peak value
4. Average value