Equipotential: ΔV = 0 ⇒ W = qΔV = 0. Electric field perpendicular to equipotentials. Memory aid: 'Equipotential: no work to move charge along it'. Electrostatics concept frequently tested in competitive exams.
Explanation:
Resistance R = V²/P = 220²/100 = 484 Ω. At 110 V, P = V²/R = 110²/484 = 12100/484 = 25 W. Assuming resistance constant. Power reduces to quarter when voltage halved (P ∝ V² for fixed R).
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