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The output power in a step-up transformer is _____.

Asked in GSEB Board July 2017 · Transformers

Answer: (4) less than the input power

Step-by-step solution

Idea: a transformer passes energy from the primary to the secondary through a changing magnetic flux; it cannot add energy.

In a real transformer some input power is always lost: I²R heating of the copper windings, eddy currents and hysteresis in the iron core, and flux leakage.

So Pₒᵤₜ=Pᵢₙ-Pₗₒₛₛ, and the efficiency η=(Pₒᵤₜ)/(Pᵢₙ) is less than 1.

Stepping up the voltage steps the current down; it does not raise the power.

So the output power is less than the input power.

Why the other options are wrong

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