Question
A torch bulb rated as 4.5 W, 1.5 V is connected as shown in the figure. The emf of the cell needed to make the bulb glow at full intensity is
Answer: Option D
:
D
When bulb glows with full intensity, potential difference across it is 1.5 V. So current through the bulb and resistance of 1Ω are 3 A and 1.5 A respectively. So main current from the cell i = 3 + 1.5 = 4.5 A. By using E=V+ir⇒E=1.5+4.5×2.67=13.5V.
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:
D
When bulb glows with full intensity, potential difference across it is 1.5 V. So current through the bulb and resistance of 1Ω are 3 A and 1.5 A respectively. So main current from the cell i = 3 + 1.5 = 4.5 A. By using E=V+ir⇒E=1.5+4.5×2.67=13.5V.
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