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 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

An ideal transformer must step 960 V down to 120 V. Its primary winding has 160 turns. How many turns N₂ does the secondary winding need?

V₁ = 960 VV₂ = 120 VN₁ = 160

N₂ =

2.Easy

An ideal transformer must step 4600 V down to 230 V. Its primary winding has 1000 turns. How many turns N₂ does the secondary winding need?

V₁ = 4600 VV₂ = 230 VN₁ = 1000

N₂ =

3.Medium

An amplifier with an output resistance of 640 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 640 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 640 ΩR_L = 10 Ω

a =

4.Medium

A 50 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 4:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 4:1R_L = 50 Ω

R_1′ = Ω

5.Hard

A single-phase 75 kVA transformer has a core loss of 600 W. At rated load and a power factor of 0.9 lagging its efficiency is 97%. Find the full-load copper loss P_cu,fl in watts.

S = 75 kVAP_core = 600 Wpf = 0.9η = 97%

P_cu,fl = W

6.Hard

A single-phase 25 kVA transformer has a core loss of 125 W. At rated load and a power factor of 0.95 lagging its efficiency is 97.5%. Find the full-load copper loss P_cu,fl in watts.

S = 25 kVAP_core = 125 Wpf = 0.95η = 97.5%

P_cu,fl = W

Answer key

1. N₂ = 20
2. N₂ = 50
3. a = 8
4. R_1′ = 800 Ω
5. P_cu,fl = 1488 W
6. P_cu,fl = 484 W

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