# Solar energy flux, Earth's population

1. Sep 28, 2004

### phy

Solar energy flux, Earth's population....

Hi everyone

I have this one question from my optics course that has me totally stumped. It reads "Solar energy flux at Earth's position is about 1.7kW/m^2. Estimate the maximum possible population of the Earth." :surprised

I've looked through my textbook and asked a few people in my class but nobody has been able to come up with anything. Apart from one equation that I found (J=0.25n<c> where J is molecular flux, n is the particle number density and c is the mean molecular speed), I couldn't even start the question. If somebody could maybe just throw out some hints or equations, it would be greatly appreciated. Thanks

2. Sep 28, 2004

### phy

Can somebody please help me? I don't want anybody to do it for me. Just give me a hint on which direction I should be going in. Lol please? Thanks =)

3. Sep 28, 2004

### Claude Bile

Estimate how much energy, per second, a human needs to stay alive, that is, how much energy a human metabolises in one second.

For extra complexity, you can estimate an energy conversion efficiency, i.e. the percentage of energy incident on the Earth that is converted into energy useful to humans.

Hope that gets you going.

Claude.

4. Sep 28, 2004

### phy

Uhhhh that actually makes sense but how much energy does the average human metabolize per second?

Does 2500 Calories sound resonable?

Last edited by a moderator: Sep 28, 2004
5. Sep 29, 2004

### Claude Bile

10,000 kJ/day is probably reasonable to a first approximation. In a question like this, you are not looking for precision, just a ball park figure.

Claude.

6. Sep 29, 2004

### phy

Okie dokie I think I know how to do the question. Thanks a lot for your help