Answer:
The answer is below
Explanation:
The inverse fourth power law states that the intensity varies inversely to the fourth power of the distance from the source. That is as the distance increases, the intensity decreases.
Let I represent the intensity and let d represent the distance from the source, hence:
I ∝ 1 / d⁴
I = k / d⁴
Where k is the constant of proportionality.
Given that at a power of 25W = 25*10⁻⁶ W, the distance (d) = 225 m. We can find the value of k.
25*10⁻⁶ = k / 225⁴
k = 225⁴ * 25*10⁻⁶ = 64072.27
Hence:
I = 64072.27 / d⁴
At a distance (d) = 0.9km = 900 m, we can find the corresponding power:
I = 64072.27 / 900⁴
I = 9.77 * 10⁻⁸ W
