AC power & power factor worksheet with answers

Free printable AC power & power factor worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
P = ?QS = V·Iφ

A single-phase load draws 9 A (rms) from a 400 V (rms) supply at a power factor of 0.6 lagging. Find the real power P it takes.

V = 400 VI = 9 Apf = cos φ = 0.6
P = W
2.Easy
120 Vload13 kW, 5.5 kvarI = ?

A single-phase load connected to a 120 V supply takes 13 kW and 5.5 kvar. Find the current I drawn from the supply.

V = 120 VP = 13 kWQ = 5.5 kvar
I = A
3.Medium
P = 34 kWQSφ

A single-phase motor takes 34 kW at a power factor of 0.75 lagging from a 240 V supply. Find the line current I.

P = 34 kWpf = 0.75V = 240 V
I = A
4.Medium
120 VZ6 + j8 ΩI

A load with impedance Z = 6 + j8 Ω is connected to a 120 V (rms) single-phase supply. Find the apparent power S.

V = 120 VZ = 6 + j8 Ω
S = VA
5.Hard
P = 40 kWQ1​S1​φ1​QC​

A single-phase load takes 40 kW at a power factor of 0.8 lagging from a 400 V, 60 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the reactive power QC the capacitor must supply.

P = 40 kWpf1 = 0.8pf2 = 0.98V = 400 Vf = 60 Hz
QC = kvar
6.Hard
400 V60 Hzload7 kW, 0.75C33 µFI

A single-phase load takes 7 kW at a power factor of 0.75 lagging from a 400 V, 60 Hz supply. A 33 µF capacitor is connected in parallel with the load. Find the new power factor cos φ seen by the supply.

P = 7 kWpf1 = 0.75V = 400 Vf = 60 HzC = 33 µF
cos φ =

Answer key

  1. 1. P = 2160 W
  2. 2. I = 117.6 A
  3. 3. I = 188.9 A
  4. 4. S = 1440 VA
  5. 5. QC = 21.88 kvar
  6. 6. cos φ = 0.8584

Full step-by-step solutions: practise this topic on examproblems.com.