# Homework Help: What is the solar constant in certain area of earth per day?

1. May 24, 2014

### viniterranova

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

The solar constant, the amount of solar energy reaching the Earth per unit time and area above the atmosphere and an
element of area perpendicular to the direction from sunlight is 1.36 kW / m². For an element of area whose normal
makes a angle q with the direction of the solar rays, the energy flow varies with cos theta.
a) Calculate the total amount of solar energy reaching the Earth per day.

Solar Constat I=1.36 kW/m^2

2. Relevant equations

Q=C*m*ΔT

3. The attempt at a solution

From the equation above I wrote,
Q=Δt*C*S*cos Θ

Intregrating, taking a small infinitesimal.

dQ=C*Δt*dS*cos Θ

Q=C*Δt∫cos Θ*dS.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 24, 2014

### Staff: Mentor

This is just geometry, you don't have to integrate anything (you can, but it just makes the problem more complicated). As seen from the sun, how does the earth look like?

3. May 24, 2014

### viniterranova

Someone said that I should integrate it. So, if not for me the earth is like a ideal point.

4. May 24, 2014

### dauto

No, not a point. A point is too small to represent the view of the Earth. Look at a picture of the earth what does it look like? By the way, the formula you provided in the "Relevant equations" section is completely irrelevant. One more thing, that should've been posted in the "Introductory Physics Homework" forum.

5. May 24, 2014

### viniterranova

So, what is the way to solve the problem?

6. May 24, 2014

### Staff: Mentor

See post #2:
Certainly not like a single point!

7. May 24, 2014

### dauto

One step at a time. Before solving the problem you have to first understand the problem. Let put if a different way. The amount of light collected by the earth depends on how large a target the earth is. That's why we asked what the earth looks like from the point of view of the sun to which you responded "a point", but that makes no sense so you should try again instead of just ask "So, what is the way to solve the problem?" You're supposed to show some effort.

8. May 26, 2014

### viniterranova

In this case, I think the earth´s half circunference x one meter.

9. May 26, 2014

### Staff: Mentor

Why one meter?
What's the relevance of "1 meter" for the shape of earth?

If you look at the moon, how does it look like? Can you describe the shape?

10. May 26, 2014

### dauto

That doesn't mean anything. It's not even wrong. It's just meaningless