Question

Intensity of light due to a point source at a distance to metres is 20 units the intensity due to the same source at a distance of 4 metre is

Answer 1

r1=20m

I1=20

I2= ? ans 5

r2=r1SQrtI1/I2

i 2 =4

Answer 2

Hey dear,

◆ Answer-
500 units

◆ Explaination-
# Given-
d1 = 20 m
d2 = 4 m
I1 = 20 units

# Solution-
According to inverse square law, intensity of light is inversely proportional to distance.
I ∝ 1/d^2

Therefore,
I1 / I2 = d2^2 / d1^2
I2 = I1.d1^2 / d2^2
I2 = 20 × 20^2 / 4^2
I2 = 500 units.

Intensity of light at distance of 4 m from given point source is 500 units.

Hope this is helpful...