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
120 Vload23 kW, 16.5 kvarI = ?

A single-phase load connected to a 120 V supply takes 23 kW and 16.5 kvar. Find the current I drawn from the supply.

V = 120 VP = 23 kWQ = 16.5 kvar
I = A
2.Easy
P = ?QS = V·Iφ

A single-phase load draws 8 A (rms) from a 120 V (rms) supply at a power factor of 0.8 lagging. Find the real power P it takes.

V = 120 VI = 8 Apf = cos φ = 0.8
P = W
3.Medium
P = 22 kWQ = ?Sφ

A single-phase motor takes 22 kW at a power factor of 0.85 lagging from a 400 V supply. Find the reactive power Q it draws.

P = 22 kWpf = 0.85V = 400 V
Q = kvar
4.Medium
240 VR + jXP = 1188 W5.5 A

An inductive load takes 5.5 A and 1188 W from a 240 V (rms) single-phase supply. Model it as a resistance R in series with a reactance X. Find R.

V = 240 VI = 5.5 AP = 1188 W
R = Ω
5.Hard
120 V50 HzRs​ = 2 ΩXs​ = j3 ΩZL​ = ?

A 120 V (rms), 50 Hz source has an internal impedance Zs = 2 + j3 Ω. The load impedance ZL can be chosen freely. Find the maximum real power Pmax that can be delivered to the load.

Vs = 120 V (rms)f = 50 HzZs = 2 + j3 Ω
Pmax = W
6.Hard
P = 5 kWQ1​S1​φ1​QC​

A single-phase load takes 5 kW at a power factor of 0.75 lagging from a 400 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the new line current Inew.

P = 5 kWpf1 = 0.75pf2 = 0.98V = 400 Vf = 50 Hz
Inew = A

Answer key

  1. 1. I = 235.9 A
  2. 2. P = 768 W
  3. 3. Q = 13.63 kvar
  4. 4. R = 39.27 Ω
  5. 5. Pmax = 1800 W
  6. 6. Inew = 12.76 A

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