Hello

This is my first post on this forum so my apologies ahead of time if I have posted it in the wrong place.

I am currently looking into the inverse square law for a point source. It is Intensity is inversely proportional to the distance from the source squared.

I then imagined the light landing on a flat plane. As the light hitting the nearest point to the plane will have traveled a shorter distance it will have a higher intensity than light hitting further along the plane.

By making a right handed triangle (see attachment) between the point source, the plane and the point of incidence of the light we can see that the relationship between the minimum distance between the light source and the plane, R, and the distance between the light source and the point of incidence, D, is:

D=R/cos(theta)

Where theta is the the angle between the two displacements (see attachment). Adding this into the inverse square law suggests that for a point source shedding light onto a flat plane the intensity is proportional to cos(theta)/r all squared.

Is this correct?

I believed it was until I found a link that suggested that only the r was squared not the cosine. It is posted below.

http://www.lepla.org/en/modules/Acti...7/m17-theo.htm
I know the problem is probably very simple but any and all help would be greatly appreciated

Thank you