Question

The operating temperature of the filament of lamp is ${2000}^{\circ }C.$ The temperature coefficient of the material of filament is $0.005{/}^{\circ }C.$ If the atmospheric temperature be $0^{\circ }C,$ the current in the 100 W and 2000 V lamp when it is switched on its nearest to :

• A. 2.5 A
• B. 0.05 A
• C. 4.5 A
• D. 5.5 A

Answer 1

The correct option is B 0.05 A

The operating temperature of the filament of lamp= ${2000}^{o}C$

The temperature coefficient of the material of filament= $0.005{/}^{o}C$

The atmospheric temperature= $0^{o}C$

The current in the $100W$ and $2000V$ when it is switched on the nearest to-

$1^{o}C=0.005$

$\therefore {2000}^{o}C=\frac{5}{1000}\times 2000=10$

$P=VI$

or, $100=2000\times I$

or, $I=\frac{100}{2000}=0.05A$ .