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 worksheet Practise 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

A single-phase load draws 20 A (rms) from a 240 V (rms) supply at a power factor of 0.7 lagging. Find the reactive power Q it takes.

V = 240 VI = 20 Apf = cos φ = 0.7

Q = var

2.Easy

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 240 V, 18.5 A and 4218 W. Find the reactive power Q taken by the load.

V = 240 VI = 18.5 AP = 4218 W

Q = var

3.Medium

Two loads are connected in parallel to a 230 V single-phase supply: a 2 kW load at a power factor of 0.85 lagging and a 9 kW load at a power factor of 0.7 leading. Find the total current I drawn from the supply.

V = 230 VP₁ = 2 kW, pf₁ = 0.85 laggingP₂ = 9 kW, pf₂ = 0.7 leading

I = A

4.Medium

A single-phase motor takes 22 kW at a power factor of 0.7 lagging from a 400 V supply. Find the reactive power Q it draws.

P = 22 kWpf = 0.7V = 400 V

Q = kvar

5.Hard

A 230 V (rms), 50 Hz source has an internal impedance Z_s = 25 + j6 Ω. The load impedance Z_L can be chosen freely. The load for maximum power is built from a resistor in series with a capacitor. Find the capacitance C.

V_s = 230 V (rms)f = 50 HzZ_s = 25 + j6 Ω

C = µF

6.Hard

A 230 V (rms), 1000 Hz source has an internal impedance Z_s = 5 + j30 Ω. The load impedance Z_L can be chosen freely. Find the maximum real power P_max that can be delivered to the load.

V_s = 230 V (rms)f = 1000 HzZ_s = 5 + j30 Ω

P_max = W

Answer key

1. Q = 3428 var
2. Q = 1386 var
3. I = 58.99 A
4. Q = 22.44 kvar
5. C = 530.5 µF
6. P_max = 2645 W

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