# MCQs on Electric Circuits

##### Page 14 of 63. Go to page 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
01․ What is referred as the average value in AC opearation?
Average of all values of an alternating quantity.
Average of all values of the phase sequences.
Average of all values of the (+)ve and (-)ve half.
Average of all values of an alternating quantity over a complete cycle.

The average value of an alternating quantity is the average of all the instantaneous values during one alternation. Since the alternating quantity increases from zero to peak value and decreases peak value to zero during one alternation. So, the average value must be some value between those two limits. We can determine the average value of an alternating quantity by adding together a series of instantaneous values of the alternation from 0° to 180° and then dividing the sum by the number of instantaneous values used. That computation would show that one alternation of a sine wave has an average value equal to 0.636 times the peak value.

02․ What is form factor?
Average value / R.M.S. value.
Average value / Peak value.
Instantaneous value / Average value.
R.M.S. value / Average value.

The form factor of an alternating current waveform (signal) is the ratio of the rms (root mean square) value to the average value. Here the average value is the mathematical mean of absolute values of all points on the waveform.

03․ Select the wave that has the least value of form factor.
Square wave.
Rectangular wave.
Triangular wave.
Sine wave.

In square wave, the rms value and average value are same (whatever peak magnitude presents in that square wave). So, the form factor is equal to one. But, in other kind of waveforms (for example, sine, triangle, rectangle, etc), the average value is less than the rms value. So, the value of form factor is greater than one. Hence, as compared to other waveforms, square wave has least value of form factor.

04․ What is the frequency of domestic power in India?
50 Hz.
60 Hz.
220 Hz.
70 Hz.

The British system tells that the domestic power supply range is 230 Volts, 50 Hz. The American system tells that the domestic power supply range is 110 / 120 Volts, 60 Hz. Since, India follows the British standard and thus the frequency of the domestic power in India is 50 Hz.

05․ What is apparent power in AC operation?
Product of voltage and current.
Product of rms voltage and rms current.
Product of voltage and current at no load.
Product of voltage and current at full load.

In an AC circuit, the product of rms voltage and rms current is called as the apparent power. When the impedance is pure resistance, the apparent power is same as the real power. But, when the reactance is added, then the apparent power is greater than the real power.

06․ What is the real power in AC operation?
VIcosφ.
Apperant power × cosφ.
Both option A and B.
None of these.

We know that the product of the voltage and current is called apparent power and the product of the voltage, current and power factor is called as the real power. From the power triangle the real power is equal to the product of the apparent power and the power factor.

07․ An electrolytic capacitor can be used for
DC only.
AC only.
both A and B.
none Of the above.

The electrolytic capacitor can be used in DC only because it is a polarized capacitor. There is a clear marking of the polarity (positive and negative) at the terminal point. We cannot use this capacitor in AC power supply because the electrolytic oxide material works in very low frequency power supply (nearly to be zero). If there is any incorrect polarization or presence of AC supply, the insulated oxide layer will break down very soon and it causes permanent damage as a result.

08․ There are two capacitors C1 and C2 in parallel , what will be their equivalent capacitance?
(C1 + C2) / C1C2.
(C1C2) / C1 + C2.
C1 + C2.
C1C2.

If we connect the capacitors in parallel, then the total capacitance can increase. Hence, the total capacitance value for parallel connected capacitor is Ceq = (C1 + C2 ...... + Cn).

09․ For making a capacitor it is better to select a dielectric having
low permittivity.
high permittivity.
permittivity same as that of air.
permittivity more than that of air.

In order to maximize the charge that a capacitor can hold, the dielectric material needs to have a high permittivity as possible. The formula for capacitance is, C = ε0A/d. So, if permittivity increases than A/d ratio can be reduced for same capacitance value and hence the size of the capacitor can be optimised.

10․ What is called the instantaneous value of an alternating current?
The value of alternating quantity at any instant.
The value of peak quantity at any instant.
The value of peak current at any instant.
The value of alternating frequency at any instant.

The instantaneous value of an alternating current is the value of current at one particular instant. The value may be zero if the particular instant is the time in the cycle at which the polarity of the current is changing. It may also be the same as the peak value, if the selected instant is the time in the cycle at which the current stops increasing and starts decreasing. There are actually an infinite number of instantaneous values between zero and the peak value.

<<<1213141516>>>