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  • A torch bulb rated 4.5 W, 1.5 V is connected as shown in Figure. The e.m.f. of the cell needed to make the bulb glow at full intensity is <img alt="" src="https://cdn.entrance360.com/medi

A torch bulb rated 4.5 W, 1.5 V is connected as shown in Figure. The e.m.f. of the cell needed to make the bulb glow at full intensity is

Option: 1

 4.5 V
 


Option: 2

 1.5 V


Option: 3

 2.67 V

 


Option: 4

 13.5 V


Answers (1)

best_answer

Resistance of bulb = \mathrm{\frac{1.5 \times 1.5}{4.5} \Omega=0.5 \Omega}
Resistance of parallel combination, \mathrm{ R=\frac{1 \times \frac{1}{2}}{1+\frac{1}{2}} \Omega=\frac{1}{3} \Omega}
Now, \mathrm{ r=\frac{E-V}{V} R \Rightarrow \frac{8}{3}=\frac{E-1.5}{1.5} \times \frac{1}{3} \Rightarrow E=13.5 \mathrm{~V}}

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Ritika Harsh

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