What is the average intensity at a distance?

[Sylvia]

Homework Statement

A 60 W bulb radiates light uniformly in all directions. What is the average intensity of the light bulb at a distance 0.40 m.

Homework Equations

I = P/A, part of my problem is that I don't know the relevant equations

The Attempt at a Solution

 

[matteo137]

Your equation is correct.
You have to assume that the bulb radiates uniformly in all directions, then the area $A$ over which the power is distributed is the surface of a sphere with radius the distance you have.

 

[Sylvia]

Thank you, that makes so much sense. I thought the area had to be of the object radiating the light.