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

Question

A torch bulb rated as 4.5 W, 1.5 V is connected as shown in the figure. The e.m.f. of the cell needed to make the bulb glow at full intensity is (A) 4.5 V (B) 1.5 V (C) 2.67 V (D) 13.5 V

Tardigrade Admin · Accepted Answer

Current in the bulb =(P/V)=(4.5/1.5)=3 A Current in 1 Ω resistance =(1.5/1)=1.5 A Hence total current from the cell i=3+1.5=4.5 A By using E=V+i r ⇒ E=1.5+4.5 ×(2.67)=13.5 V

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

4.5 V

1.5 V

2.67 V

13.5 V

Current in the bulb $= \frac{P}{V} = \frac{4.5}{1.5} = 3 A$
Current in $1 Ω$ resistance $= \frac{1.5}{1} = 1.5 A$
Hence total current from the cell $i = 3 + 1.5 = 4.5 A$
By using $E = V + i r$
$\Rightarrow E = 1.5 + 4.5 \times (2.67) = 13.5 V$

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