1. If the 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
Answer: B
We know, the 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
Answer: D
The instantaneous value of a sinusoidally 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
Answer: A
Average current = ∫0πidθ/π
= ∫0πImsinθ 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
Answer: B
Irms2 = ∫0πdθ i2/2π = Im2/2
Irms = Im/√2.
5. Average value of current over a full cycle is?
A. 0.67Im
B. 0
C. 6.7Im
D. 3.3Im
Answer: B
The average of sine or cosine over a period is zero so, the average value of current over a full cycle is zero.
6. What is the correct expression for the form factor?
A. Irms × Iav
B. Irms / Iav
C. Irms + Iav
D. Irms – Iav
Answer: B
The correct expression for the form factor is Irms/Iav where Irms is the RMS value of the current and Iav 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
Answer: C
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
Answer: C
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 the sinusoidal current?
A. π/2
B. π/4
C. 2π
D. π/√2
Answer: A
For sinusoidal current, Irms = Im/√2
Iav = √2 Im/π
So, form factor = Irms/Iav = 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
Answer: A
We know that 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.
