# Homework Help: Energy/Solar Energy

1. Feb 4, 2014

### student123

Hi, so I have been asked to find an expression that governs the rate of solar energy incident upon the Earth, if the Earth lies at a distance, D from the Sun of 1.5x10^11 m, and the Earth has a radius, RE. I also know the Sun has a power output of about 4x10^26 watts.

At this point I have considered looking at P = W/T, I think the main issue is I have no clue what the rate of solar energy incident upon the Earth is supposed to look like written out in equation form. I know the question is asking the rate at which the Earth absorbs energy from the sun, but I'm not sure what to do or where to go from here. Please help me! Thank you!

2. Feb 5, 2014

### CWatters

The answer will have units "Watts per square meter".

Imagine a glass sphere of radius D surrounding the sun. All the light from the sun must pass through that sphere. It has area = ??. The earth blocks what fraction of that area?

3. Feb 5, 2014

### haruspex

My reading is that it's the total power incident on the Earth that's required, so that will be in Watts.
Not useful here since there is no mention of an amount of work or a period of time. Just follow CWatters' hint.

4. Feb 5, 2014