# What is the average intensity at a distance?

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1. Mar 4, 2015

### Sylvia

1. The problem statement, all variables and given/known data
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.

2. Relevant equations
I = P/A, part of my problem is that I dont know the relevant equations

3. The attempt at a solution

2. Mar 4, 2015

### 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.

3. Mar 4, 2015

### Sylvia

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

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