Question

the light intensity of a source is 100 Candelas. The illuminance on a surface is 4 Lux. How far is the surface from the source

Answer 1

The answer is: 5 meters 

Answer 2

The surface from the source is 5 m.

Step-by-step explanation:

Given that,

Light intensity = 100 candelas

Illuminance = 4 lux

The formula of illumination is

According to illumination law,

The intensity of illuminance of the the light source is inversely proportional to the square of the distance from the source.

The formula of illumination is

`E\propto(1)/(d^2)`

`E=(I)/(d^2)`

Where, E = illuminance

I = luminous Intensity of the light

D = distance

We substitute the value into formula

`d^2=(I)/(E)`

`d^2=(100)/(4)`

`d^2=25`

`d = 5\ m`

Hence, The surface from the source is 5 m.