When exposed to a 10 W source for 12 s , a photographic plate records sufficiently intense lines. To obtain equally intense lines, what should be the exposure time for a 12 W source that radiates light of the same colour?

Step-by-step solution

The intensity of the lines on a photographic plate is determined by the total light energy received, which is the product of the power of the source and the exposure time. For equally intense lines, the total energy must be the same in both cases. E₁ = E₂ P₁ t₁ = P₂ t₂ Given P₁ = 10 W , t₁ = 12 s , and P₂ = 12 W . 10 12 = 12 t₂ t₂ = 120 12 = 10 s