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An incandescent lamp is marked 40W, 240V. If resistance at room temperature (26°C) is 120 Ω and temperature coefficient of resistance is 4.5 × 10– 3/°C , then its ‘ON ’ state filament temperature in °C is approximately ___________.
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- 1171
- 2471
- 1417
- All of the above
Correct Option: B
P = 40 W
V = 240V
| Now , Rlamp = | = | = 1440 Ω | ||
| P | 40 |
AT t = 26 °, R = 120W and α = 4.5 × 10– 3/ °C
Now Rlamp = R[1 + α (t2 – t1)]
∴ 1440 = 120[ 1 + 4.5 × 10– 3 (θ2 - 26)]
t2 = 2470.44 °C
