Question

The intensity of a point source of light, S, placed at a distance d in front of a screen A, is I₀ at the center of the screen. Find the light intensity at the center of the screen if a completely reflecting plane mirror M is placed at a distance d behind the source, as shown in the figure.

Options

• `(27  "I"_0)/9`

• `(25  "I"_0)/9`

• `(17  "I"_0)/9`

• `(10  "I"_0)/9`

Answer 1

`(10  "I"_0)/9`

Explanation:

E₁ = I₀ = `"L"/"d"^2`, without mirror

and E₂ = `"L"/"d"^2 + "L"/(3"d")^2 = "L"/"d"^2[1 + 1/9] = (10  "I"_0)/9` with mirror