Stray Loss at Maximum Efficiency

Correct Answer

B — 1600 W

Concept and Reasoning

At the stated operating point, armature current is Ia=(E−V)/Ra=(240−220)/0.25=80 A. Maximum efficiency occurs when variable copper loss equals constant/stray loss, so stray loss=Ia²Ra=80²×0.25=1600 W. This matches option B.

Calculation / Key Relation

Ia=(240−220)/0.25=80A

stray loss=Ia²Ra=1.6kW

Exam Takeaway

Maximum efficiency condition: variable copper loss = constant loss.

Common Mistake

Use induced emf minus terminal voltage to obtain generator armature current.