If voltage across a bulb (rated 220 V, 100 W) drops by 2.5% of its rated value, the percentage by which its power would decrease is:
Options

Question

If voltage across a bulb (rated 220 V, 100 W) drops by 2.5% of its rated value, the percentage by which its power would decrease is:

G1 Physics · Accepted Answer

Step 1: Treat bulb resistance as constant: P = V²/R. Step 2: New voltage V′ = 0.975V. Step 3: P′/P = (0.975)² = 0.950625. Percentage loss ≈ 4.94%, about 5%.