Question

A photographic plate records suffciently intense lines when it is exposed for 12 s to a source of 10 W. source radiating the light of same colour to get equal intense lines ?

Answer 1

To get equal intense lines on the photographic plate, the radiant flux (energy) should be same

So, $10W\times 12sec=12W\times t$

$\Rightarrow t=\frac{10W\times 12sec}{12W}$

$=10sec$