Peak and RMS values of alternating current and voltage — practice questions

Question 1 · difficulty L1 · recall

For a sinusoidal current i=I0 sinωt, I0 is the

• A. peak current
• B. RMS current
• C. average over a full cycle
• D. frequency

Question 2 · difficulty L1 · understanding

The RMS value of a sinusoidal current with peak I0 is

• A. sqrt(2)I0
• B. I0/sqrt(2)
• C. I0/2
• D. 2I0/π

Question 3 · difficulty L2 · understanding

The RMS value of a sinusoidal voltage with peak V0 is

• A. V0
• B. 2V0/π
• C. V0/sqrt(2)
• D. sqrt(2)V0

Question 4 · difficulty L2 · application

A 230 V AC mains rating normally refers to approximately

• A. 230 V peak
• B. 230 V peak-to-peak
• C. 230 V average over a full cycle
• D. 230 V RMS

Question 5 · difficulty L3 · application

A sinusoidal current has RMS value 5 A. Its peak value is

• A. 5sqrt(2) A
• B. 5/sqrt(2) A
• C. 10 A
• D. 2.5 A

Question 6 · difficulty L3 · application

The average value of an ideal sinusoidal current over one complete cycle is

• A. I0/√2
• B. zero
• C. 2I0/π
• D. I0

Question 7 · difficulty L4 · analysis

Why is RMS current useful for power calculations in a resistor?

• A. It equals the largest instantaneous current
• B. It is always the arithmetic average of current
• C. It gives the same average heating as an equal DC current
• D. It makes resistance vanish

Question 8 · difficulty L4 · analysis

A sinusoidal voltage has peak 100sqrt(2) V. Its RMS value is

• A. 200 V
• B. 50 V
• C. 100sqrt(2) V
• D. 100 V

Question 9 · difficulty L5 · analysis

If the peak current is doubled while resistance is unchanged, average heating power in a resistor becomes

• A. four times
• B. twice
• C. half
• D. unchanged

Question 10 · difficulty L5 · analysis

Two sine-wave currents have equal RMS values but frequencies f and 2f through the same pure resistor. Their average powers are

• A. in the ratio 1:2
• B. equal
• C. in the ratio 1:4
• D. zero for the higher frequency