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STANDARDPhysics-Electromagnetic Induction

STANDARD Physics Transformers MCQ Question

Type: MCQ-numerical-Medium-Class 12

The current drawn by the primary of a transformer, which steps down 200 V to 20 V to operate a device of resistance 20 Ω is (Assume the efficiency of the transformer to be 80%)

A

0.125 A

B

0.225 A

C

0.325 A

D

0.425 A

Correct Answer

Option A

Detailed Explanation

Given: Vₚ = 200 V, R = 20 Ω, Vₛ = 20 V, η = 80%. Current through the secondary coil is Iₛ = Vₛ/R = 20V/20Ω = 1A. Efficiency of transformer, η = Output power/Input power = VₛIₛ/VₚIₚ. Solving for Iₚ gives Iₚ = VₛIₛ/(Vₚη) = 20 × 1 × 100 / (200 × 80) = 0.125 A.

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