Rate of Heat Absorption from Visible vs Infrared Light

In summary, the radiometer spun faster under a 100 W 2360 lm bulb than a 100 W 1600 lm bulb. This may be because the 2360 lm bulb emits radiation with a higher frequency than the 1600 lm bulb.
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I recently did an experiment with the Crookes's Radiometer.

The radiometer was first placed under a 100W 1600 lm bulb and then a 100 W 2360 lm bulb. Though they both emit the same energy, the radiometer spun about 30% faster under the 2360 lm.

Why is this? I was thinking maybe this was because visible light is absorbed faster than the infrared, but don't know for sure.

Thanks,

sphoenixee
 
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  • #2
You're right. In general, the amount of energy absorbed by a surface depends on both the intensity and spectrum of the radiation hitting it.
 
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Just to clarify, it's the higher the spectrum, the higher the absorption rate?
 
  • #4
Just to clarify, it's the higher the spectrum, the higher the absorption rate?

What do you mean by "higher the spectrum" - more intensity or higher frequency?
 
  • #5
What do you mean by "higher the spectrum" - higher frequency or higher intensity?

In the case of frequency, there is no simple relationship - it depends specifically on the composition of the material.
 
  • #6
Sorry about all the repeated messages. I was experiencing internet problems so I couldn't tell what went through.
 
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My bad, but yes, I meant the higher the frequency. So the relationship between absorption rate and frequency is empirical? Or is there just a complicated relationship? Does anyone know of any good articles about this?

Thanks,

sphoenixee
 
  • #8
It is not quite empirical. There is a lot of theory there, but it is quite complicated, depending on the composition of the surface as well as the frequency of the radiation. the simplest example would be the fact that a red surface reflects red and absorbs other colors, while a blue surface reflects blue and absorbs others (this is overly simplified). Different parts of the spectrum (ranging from radio waves to gamma rays) alll act differently. Low frequency such as microwaves interact with molecules, while higher frequencies such as gammma rays interact with electrons and nuclei.
 
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  • #9
Thanks for clearing that up mathman!
 

1. What is the difference between visible and infrared light?

Visible light is the portion of the electromagnetic spectrum that is visible to the human eye and is made up of colors ranging from red to violet. Infrared light, on the other hand, is invisible to the human eye and has longer wavelengths than visible light.

2. How does the rate of heat absorption differ between visible and infrared light?

The rate of heat absorption differs between visible and infrared light because they have different wavelengths and energies. Infrared light has longer wavelengths and lower energies, which makes it more easily absorbed by objects and can cause an increase in their temperature.

3. Which type of light is more effective in heating objects?

Infrared light is more effective in heating objects because it has longer wavelengths and lower energies, which means it can penetrate deeper into objects and cause a greater increase in temperature compared to visible light.

4. Can both visible and infrared light be absorbed by the same object?

Yes, both visible and infrared light can be absorbed by the same object. However, the rate of absorption may differ depending on the object's properties and the intensity and wavelength of the light.

5. How does the rate of heat absorption from visible vs infrared light affect the Earth's climate?

The rate of heat absorption from visible and infrared light plays a crucial role in the Earth's climate. Infrared light, being more easily absorbed by objects, contributes to the greenhouse effect and helps regulate the Earth's temperature. Visible light, on the other hand, is reflected by the Earth's surface and helps to keep the planet cool.

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