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If the current in an electric bulb increases by 2%, what will be the change in the power of the bulb? (Assume that the resistance of the filament of the bulb remains constant.)

Asked in GSEB Board March 2018 · Heating and power in resistors

• (1) decreases by 2%
• (2) decreases by 4%
• (3) increases by 2%
• (4) increases by 4%

Step-by-step solution

Why the other options are wrong

• (1) Power cannot fall when the current through a fixed resistance rises, because P = I²R grows with I. It also copies the 2% of the current instead of doubling it.
• (2) Right size, wrong direction: with R fixed, P = I²R increases when I increases.
• (3) Treats power as proportional to current. With R constant, P∝ I², so the fractional change doubles: 2×2% = 4%.

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