The intensity of light (L) from a given source is inversely proportional to the square of the distance (D) from it. At a distance of 25 m, a light has an intensity of 64 candelas (CD). Find the intensity of light at a point 20 m from the source.

Answer 1

Let I represent the intensity of light at a point 20 m from the source.

According to the given information, intensity (L) is inversely proportional to the square of the distance (D) from the source. This can be written as:

L = k/D^2

where k is a constant.

We can use the given information to find the value of k. At a distance of 25 m, the light has an intensity of 64 candelas (CD):

64 = k/25^2

Simplifying:

64 = k/625

k = 64 * 625
k = 40000

Now we can use this value of k to find the intensity at a point 20 m from the source:

I = 40000/20^2
I = 40000/400
I = 100 CD

Therefore, the intensity of light at a point 20 m from the source is 100 candelas (CD).