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# Basic Electrical Engineering MCQ’s – Average and RMS Values of Sinusoidal & Non-Sinusoidal Currents and Voltages

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

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Answer: b

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

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

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

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Answer: d

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

Average value of current over a half cycle is?

a) 0.67Im

b) 0.33Im

c) 6.7Im

d) 3.3Im

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Answer: a

Explanation: Average current = ∫_{0}^{π}idθ/π = ∫_{0}^{π}Imsinθ dθ/π = 2Im/π =0.67 Im.

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

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Answer: b

Explanation: I_{rms}^{2} = ∫_{0}^{π}dθ i^{2}/2π = Im^{2}/2

I_{rms}=Im/√2.

Average value of current over a full cycle is?

a) 0.67Im

b) 0

c) 6.7Im

d) 3.3Im

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Answer: b

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

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}

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Answer: b

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.

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

a) Greater than

b) Less than

c) Equal to

d) Not related to

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Answer: c

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

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

a) Greater than

b) Less than

c) Equal to

d) Not related to

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Answer: c

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

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

a) π/2

b) π/4

c) 2π

d) π/√2

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Answer: a

Explanation: For sinusoidal current, I_{rms}=Im/√2

I_{av}=√2 Im/π

So, form factor = I_{rms}/I_{av} = π/2.

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

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Answer: a

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.