Question

At what distance from the Sun is the intensity of sunlight three times the value at the Earth? (The average Earth-Sun separation is 1.496 x 10¹¹ m.)

Answer 1

The intensity (I) with distance (r) varies as

Therefore, we can write  

Let the intensity of the Sun at Earth is I₁ and its distance from the Sun is r₁ and the distance of the point, wher intensity is of 3 times of at Earth, is r₂.

Therefore, we can write

  

or,   

or,

Hence, at a distance of 0.864 X 10¹¹ m from the Sun, the intensity of sunlight will be three times the value at the Earth.