# Is this question on Intensity of light from Sun correct?

## Homework Statement  ## The Attempt at a Solution

This is an example given in the book . But I am just wondering whether the question itself is correct .

How can intensity of light emitted from Sun is given a constant ? Shouldn't 1400 be the power emitted from Sun ?

If 1400 is power emitted from sun , then in part b) , n = 1400/E . We don't need radius of earth to answer part b) .

Instead we would require radius of orbit of earth to answer part a) .

This is different from what is done in the book .

Could the experts kindly let me know whether my objection is valid or not ?

## Answers and Replies

Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
How can intensity of light emitted from Sun is given a constant ?
It is given at the Earth's orbit. There it is a given number. If you were closer to the Sun, this number would be higher.

Could the experts kindly let me know whether my objection is valid or not ?
It is not.

• Jahnavi
Charles Link
Homework Helper
Gold Member
2020 Award
Irradiance ## E=1400 \, watts/m^2 ##. The number is correct. That is the intensity (irradiance) at the earth's surface. ## \\ ## Meanwhile the sun is about 865,000 miles in diameter and is 93,000,000 miles away. The total power ## P ## satisfies ## \frac{P}{4 \pi s^2} =E## where ## s=93,000,000 \, miles ## which is ## s=1.50 \cdot 10^{11} \, m ##.

• Jahnavi
Thanks !

• Charles Link