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.

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1.Easy
240 VloadP = 480 W2.5 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 240 V, 2.5 A and 480 W. Find the reactive power Q taken by the load.

V = 240 VI = 2.5 AP = 480 W
Q = var
2.Easy
120 VloadP = 252 W3.5 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 120 V, 3.5 A and 252 W. Find the power factor cos φ of the load.

V = 120 VI = 3.5 AP = 252 W
cos φ =
3.Medium
230 VZ9 + j12 ΩI

A load with impedance Z = 9 + j12 Ω is connected to a 230 V (rms) single-phase supply. Find the reactive power Q it absorbs.

V = 230 VZ = 9 + j12 Ω
Q = var
4.Medium
230 VZ12 + j16 ΩI

A load with impedance Z = 12 + j16 Ω is connected to a 230 V (rms) single-phase supply. Find the reactive power Q it absorbs.

V = 230 VZ = 12 + j16 Ω
Q = var
5.Hard
P = 25 kWQ1​S1​φ1​QC​

A single-phase load takes 25 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 0.95. Find the new line current Inew.

P = 25 kWpf1 = 0.75pf2 = 0.95V = 400 Vf = 50 Hz
Inew = A
6.Hard
120 V60 HzRs​ = 50 ΩXs​ = j6 ΩZL​ = ?

A 120 V (rms), 60 Hz source has an internal impedance Zs = 50 + j6 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 = 60 HzZs = 50 + j6 Ω
Pmax = W

Answer key

  1. 1. Q = 360 var
  2. 2. cos φ = 0.6
  3. 3. Q = 2821 var
  4. 4. Q = 2116 var
  5. 5. Inew = 65.79 A
  6. 6. Pmax = 72 W

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