A circular area of radius 1.0 cm is placed at a distance of 2.0 m from a point source. The source emits light uniformly in al directions. The line joining the source to the center of the area is normal to the area. It is found that `2.0xx1^-3` lumen of luminous flux is incident on the area. Calculate the total luminous flux emitted by the source and the luminous intensity of the source along the axis of the area.

Explanation

Thesoid angle subtended by the area on the point source is
`/_\omega=(pi(1.0cm)^2)/((2.0m)^2)=pi/4xx10^-4sr`.
Thus `2.0xx10^-3` lumen of flux is emitted in `pi/4xx10^-4` sr. The total solid angle at the source is 4pi. As the source radiates uniformly in all directions, the total luminous flux is
`F=(4pi)/(pi/4xx10^-4)xx2.0xx10^-3lumen`
`=320 lumen.
the luminous intensity =/_\F//_\omega`
`=(2.0xx10^-3lumen)/(pi/4xx10^-4sr)=25cd`