This set of Basic Electrical Engineering Questions and Answers for Entrance exams focuses on “Average and RMS Values of Sinusoidal & Non-Sinusoidal Currents and Voltages”.

1. If maximum value of current is 5√2 A, what will be the value of RMS current?

a) 10 A

b) 5 A

c) 15 A

d) 25 A

View Answer

Explanation: We know, value of RMS current =value of max current/√2

Substituting the value of max current we get, rms current = 5A.

2. If Im is the maximum value of a sinusoidal voltage, what is the instantaneous value?

a) i=Im/2

b) i=Imsinθ

c) i=Imcosθ

d) i=Imsinθ or i=Imcosθ

View Answer

Explanation: The instantaneous value of a sinusoidal varying current is i=Imsinθ or i=Imcosθ where Im is the maximum value of current.

3. Average value of current over a half cycle is?

a) 0.67Im

b) 0.33Im

c) 6.7Im

d) 3.3Im

View Answer

Explanation: Average current = ∫

_{0}

^{π}idθ/π = ∫

_{0}

^{π}Imsinθ dθ/π = 2Im/π =0.67 Im.

4. What is the correct expression for the rms value of current?

a) Irms=Im/2

b) Irms=Im/√2

c) Irms=Im/4

d) Irms=Im

View Answer

Explanation: I

_{rms}

^{2}= ∫

_{0}

^{π}dθ i

^{2}/2π = Im

^{2}/2

I

_{rms}=Im/√2.

5. Average value of current over a full cycle is?

a) 0.67Im

b) 0

c) 6.7Im

d) 3.3Im

View Answer

Explanation: Average of sine or cosine over a period is zero so, average value of current over full cycle is zero.

6. What is the correct expression for the form factor?

a) I_{rms} * I_{av}

b) I_{rms} / I_{av}

c) I_{rms} + I_{av}

d) I_{rms} – I_{av}

View Answer

Explanation: The correct expression for form factor is I

_{rms}/I

_{av}where I

_{rms}is the rms value of the current and I

_{av}is the average current.

7. For a direct current, the rms current is ________ the mean current.

a) Greater than

b) Less than

c) Equal to

d) Not related to

View Answer

Explanation: For a direct current, the mean current value is the same as that of the rms current.

8. For a direct current, the rms voltage is ________ the mean voltage.

a) Greater than

b) Less than

c) Equal to

d) Not related to

View Answer

Explanation: For a direct current, the mean voltage value is the same as that of the rms voltage.

9. What is the value of the form factor for sinusoidal current?

a) π/2

b) π/4

c) 2π

d) π/√2

View Answer

Explanation: For sinusoidal current, I

_{rms}=Im/√2

I

_{av}=√2 Im/π

So, form factor = I

_{rms}/I

_{av}= π/2.

10. If the maximum value of the current is 5√2 A, what will be the value of the average current?

a) 10/π A

b) 5/π A

c) 15/π A

d) 25/π A

View Answer

Explanation: We know, the value of the average current = value of max current *√2 /π

Substituting the value of max current we get, rms current = 10/π A.

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