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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