JEE MAIN - Physics (2005 - No. 8)
The resistance of hot tungsten filament is about $$10$$ times the cold resistance. What will be resistance of $$100$$ $$W$$ and $$200$$ $$V$$ lamp when not in use ?
$$20\Omega $$
$$40\Omega $$
$$200\Omega $$
$$400\Omega $$
ব্যাখ্যা
$$P = Vi = {{{V_2}} \over R}$$
$${R_{hot}} = {{{V^2}} \over P} = {{200 \times 200} \over {100}} = 400\Omega $$
$${R_{cold}} = {{400} \over {10}} = 40\Omega $$
$${R_{hot}} = {{{V^2}} \over P} = {{200 \times 200} \over {100}} = 400\Omega $$
$${R_{cold}} = {{400} \over {10}} = 40\Omega $$