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In a transformer the primary has 140 turns and the secondary 280 turns. If the primary current is 4 A, the secondary current is

Asked in AIEEE 2002 · Transformers

(1) 4 A
(2) 2 A
(3) 6 A
(4) 10 A

Answer: (2) 2 A

Step-by-step solution

For an ideal transformer Nₚ Iₚ=Nₛ Iₛ.

Iₛ=Iₚ(Nₚ)/(Nₛ)=4×(140)/(280)=2 A.

Why the other options are wrong

(1) Assumes the current is unchanged.
(3) Uses a wrong turns ratio.
(4) Uses a wrong turns ratio (inverted and scaled).

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