Bulbs rated 40 W, 60 W and 100 W for 220 V mains are joined in series across a 220 V supply. Which one glows most brightly?
Correct answer B. 40 W bulb
Explanation
Resistance R = V²/P is largest for the 40 W bulb. In series the same current flows through each bulb, so power I²R is greatest in the bulb with the highest resistance.
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