Energy in EM Waves problem (finding sun power output from EM wave intensity)

In summary, the conversation was about estimating the average power output of the Sun based on the amount of energy that reaches the Earth's upper atmosphere. The answer is 3.8 X 10^26 W, and the method to get there is by using the formula Intensity = Power/Area and considering the surface area of a sphere with the Sun at the center. The conversation also touched on the confusion about power and intensity in relation to previous chapters in a book and how to take into account the Earth's orbit in the calculation. Ultimately, the correct answer was reached with the help of others.
  • #1
confusedbyphysics
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Hi, if someone could help me figure this out I'd really appreciate it.

Estimate the average power output of the Sun, given that about 1350 W/m^2 reaches the upper atmosphere of the Earth.

I know the answer is 3.8 X 10^26 W but I don't know how to get there. I've tried different equations and putting random numbers together but it's been waaayyy off. Can someone help point me in the right direction?? THANKS!
 
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  • #2
confusedbyphysics said:
Hi, if someone could help me figure this out I'd really appreciate it.

Estimate the average power output of the Sun, given that about 1350 W/m^2 reaches the upper atmosphere of the Earth.

I know the answer is 3.8 X 10^26 W but I don't know how to get there. I've tried different equations and putting random numbers together but it's been waaayyy off. Can someone help point me in the right direction?? THANKS!

The Sun emits uniformly...so the energy emitted per second gets spread over the surface of an expanding sphere. Does that give you an idea?

(do you know how the intensity of light, in W/m^2 is related to the power of a source of light?)

Patrick
 
  • #3
Assume that the sun radiates its energy into space uniformly in all directions. Now imagine a hollow sphere the size of the Earth's orbit, with the sun at the center. 1350 W of solar power strikes each m^2 of the inside surface of that sphere. Can you take it from there?
 
  • #4
No, I dont...This book is confusing, there isn't anything about power in the chapter in relation to the intensity, that's why I was looking through old chapters to see if there is a formula or something that could convert intensity into power outage. Just looking at the units, the intensity is the power of the wave over an area (m^2), right?

Do I use the surface area of the sun in the calculation somewhere?
 
  • #5
confusedbyphysics said:
No, I dont...This book is confusing, there isn't anything about power in the chapter in relation to the intensity, that's why I was looking through old chapters to see if there is a formula or something that could convert intensity into power outage. Just looking at the units, the intensity is the power of the wave over an area (m^2), right?

Do I use the surface area of the sun in the calculation somewhere?

There is a similar formula in sound waves. Intensity = power of the source / area over which the energy is spread (here, the energy is spread over the surface area of a sphere expanding away from the Sun). By the time the energy has reached the Earth, what is the area of the sphere over which the energy has spread out? And you won`t need the radius of the Sun (basically, the Sun can be treated as a point source here)
 
  • #6
the area over which the energy has spread out is over the Earth, right? surface area = 4(pi)r^2 = 5.11 X 10^8..but only part of the energy is hitting the earth, the rest is going out into the space, right?? I am lost
 
  • #7
ok if i think of the orbit of the Earth around the sun

the radius between the Earth and sun is 1.496 X10^11 m

the surface area is 4pi(r^2) which comes out to 2.81 X10^23

then if I use the equation you gave me above 1350 X (2.81 X 10^23) = 3.8 X 10^26, THE RIGHT ANSWER!

thank you both so much for your help it makes sense now
 
Last edited:

1. How is energy calculated in EM waves?

Energy in EM waves is calculated using the formula E = hf, where E is the energy, h is Planck's constant, and f is the frequency of the wave. This formula applies to all types of EM waves, including visible light, radio waves, and X-rays.

2. What is the relationship between intensity and energy in EM waves?

Intensity is a measure of the amplitude or strength of an EM wave, while energy is a measure of the wave's ability to do work. The energy of an EM wave is directly proportional to its intensity, meaning that the higher the intensity, the higher the energy.

3. Can the power output of the sun be calculated from EM wave intensity?

Yes, the power output of the sun can be calculated from EM wave intensity using the formula P = IA, where P is power, I is intensity, and A is the surface area over which the EM waves are spread. This calculation can be used to estimate the amount of energy the sun emits in the form of EM waves.

4. What factors affect the intensity of EM waves from the sun?

The intensity of EM waves from the sun can be affected by several factors, including the distance from the sun, atmospheric conditions, and the angle at which the waves hit the Earth's surface. Additionally, the sun's energy output can vary due to natural cycles and events, such as solar flares.

5. Why is it important to understand the energy in EM waves from the sun?

Understanding the energy in EM waves from the sun is important for various reasons. It helps us understand the behavior of EM waves, which are essential for technologies such as communication, satellite navigation, and medical imaging. Additionally, studying the sun's energy output can provide valuable insights into the Earth's climate and weather patterns.

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