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In an ideal step up transformer, the number of turns in primary coil and secondary coil are 100 and 200 respectively. If output current is found to be 5 A, then input current will be ________.

Asked in GUJCET 2026 · Transformers

• (1) 2.5 A
• (2) 5.0 A
• (3) 100 A
• (4) 10 A

Step-by-step solution

Why the other options are wrong

• (1) Scales the current the way the voltage scales, multiplying by (Nₚ)/(Nₛ)=(100)/(200): 5×0.5=2.5 A. Current goes in the inverse turns ratio — the coil with more turns carries less current.
• (2) Assumes a transformer passes the current straight through. It conserves power, not current: the secondary here sits at twice the voltage, so it must carry half the primary current.
• (3) No calculation with these numbers gives 100 A — it is the primary turn count Nₚ=100 copied down as a current. Sanity check: Iₚ=Iₛ(Nₛ)/(Nₚ)=5×2=10 A, and a primary current of 100 A would push in ten times the power the secondary gives out.

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