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Force exerted by radiation

  • #1

Homework Statement


The intensity of radiation reaching the earth from the sun is 1350 W/m2. The earth's radius is 6.4 × 106 m. How big a force does this radiation exert on the Earth (Assume it is all absorbed)

The Attempt at a Solution



F=AP=AI/c=2.3x109 N

That's my answer. Is that correct?

(The result in my material is 5.8x108 N)

And I want to ask one more question?
What is the difference between I or Sav and S in calculation?
If we say the Sun delivers about 10000 W/m2 of energy to the Earth's surface, so that is Sav, right?

Then they told me to calculate the total power.

I see a book solved by telling P=SavA and another book was Pav=SavA.

Which one was correct? Or was Pav the same as P?
Then is this one P=SA.
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
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hi machinarium! :smile:

your answer is 4 times too much …

did you square the diameter? :redface:

the precise equation is instantaneous power = instantaneous intensity times area …

and therefore average power = average intensity times area …

in AC electric circuits the difference between instantaneous power and average instantaneous is quite important, and with lasers also, but I don't see how you could measure instantaneous power or intensity for an incoherent source like sunlight, so that has to be average (so there's not much point in saying so) :wink:
 

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