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
PQ = ?S = V·Iφ

A single-phase load draws 15 A (rms) from a 230 V (rms) supply at a power factor of 0.8 lagging. Find the reactive power Q it takes.

V = 230 VI = 15 Apf = cos φ = 0.8
Q = var
2.Easy
PQ = ?S = V·Iφ

A single-phase load draws 13 A (rms) from a 240 V (rms) supply at a power factor of 0.9 lagging. Find the reactive power Q it takes.

V = 240 VI = 13 Apf = cos φ = 0.9
Q = var
3.Medium
120 VR + jXP = 1260 W14 A

An inductive load takes 14 A and 1260 W from a 120 V (rms) single-phase supply. Model it as a resistance R in series with a reactance X. Find R.

V = 120 VI = 14 AP = 1260 W
R = Ω
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 = 5 kWQ1​S1​φ1​QC​

A single-phase load takes 5 kW at a power factor of 0.6 lagging from a 400 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.92. Find the new line current Inew.

P = 5 kWpf1 = 0.6pf2 = 0.92V = 400 Vf = 50 Hz
Inew = A
6.Hard
P = 25 kWQ1​S1​φ1​QC​

A single-phase load takes 25 kW at a power factor of 0.65 lagging from a 240 V, 60 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the capacitance C needed.

P = 25 kWpf1 = 0.65pf2 = 0.98V = 240 Vf = 60 Hz
C = µF

Answer key

  1. 1. Q = 2070 var
  2. 2. Q = 1360 var
  3. 3. R = 6.429 Ω
  4. 4. S = 1440 VA
  5. 5. Inew = 13.59 A
  6. 6. C = 1112 µF

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