Transformers worksheet with answers

Free printable Transformers 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
N1​ = 640N2​ = ?3840 V240 V

An ideal transformer must step 3840 V down to 240 V. Its primary winding has 640 turns. How many turns N2 does the secondary winding need?

V1 = 3840 VV2 = 240 VN1 = 640
N2 =
2.Easy
N1​ = 1200N2​ = 150960 VV2​ = ?

An ideal transformer has 1200 turns on its primary winding and 150 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V2.

N1 = 1200N2 = 150V1 = 960 V
V2 = V
3.Medium
16 ΩN1​N2​1024 Ω

An amplifier with an output resistance of 1024 Ω drives a 16 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 1024 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 1024 ΩRL = 16 Ω
a =
4.Medium
10 ΩN1​N2​160 Ω

An amplifier with an output resistance of 160 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 160 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 160 ΩRL = 10 Ω
a =
5.Hard
pf 0.8150 kVA, 25% load

A single-phase 150 kVA transformer has a core loss of 450 W and a copper loss of 900 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 150 kVAPcore = 450 WPcu,fl = 900 Wx = 0.25pf = 0.8
Ploss = W
6.Hard
pf 0.85250 kVA, 75% load

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 3750 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.85 lagging. Find the total losses Ploss in watts at this load.

S = 250 kVAPcore = 1250 WPcu,fl = 3750 Wx = 0.75pf = 0.85
Ploss = W

Answer key

  1. 1. N2 = 40
  2. 2. V2 = 120 V
  3. 3. a = 8
  4. 4. a = 4
  5. 5. Ploss = 506.3 W
  6. 6. Ploss = 3359 W

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