Question

A small light source located 1 m in front of a 1-m2 opening illuminates a wall behind. If the wall is 1 m behind the opening (2 m from the light source), the illuminated area covers 4 m2. How many square meters are illuminated if the wall is 3 m from the light source? 5 m? 10 m?

Answer 1

3 m : 9 m² ; 5m: 25 m² ; 10 m : 100 m²

Step-by-step explanation:

If we assume that the light source behaves like as a point source, the light emitted by the source propagates through the space in all directions equally, which means that it obeys an inverse square law, as a consequence of our universe being 3D.

So, if at 1 m from the source, the illumination covers 1m², at 2m, it will cover 4 m², at 3m 9m², at 5 m 25 m², and at 10 m, 100 m2.