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.

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1.Easy

An ideal transformer has 80 turns on its primary winding and 400 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 400V₁ = 120 V

V₂ = V

2.Easy

An ideal transformer has 50 turns on its primary winding and 1000 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 50N₂ = 1000V₁ = 400 V

V₂ = V

3.Medium

A 4 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 3:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 3:1R_L = 4 Ω

R_1′ = Ω

4.Medium

An amplifier with an output resistance of 720 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 720 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 720 ΩR_L = 5 Ω

a =

5.Hard

A single-phase 500 kVA transformer has a core loss of 1500 W and a copper loss of 3750 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 1500 WP_cu,fl = 3750 W

S_η,max = kVA

6.Hard

A single-phase 50 kVA transformer has a core loss of 300 W and a copper loss of 1200 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 300 WP_cu,fl = 1200 W

S_η,max = kVA

Answer key

1. V₂ = 600 V
2. V₂ = 8000 V
3. R_1′ = 36 Ω
4. a = 12
5. S_η,max = 316.2 kVA
6. S_η,max = 25 kVA

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