Absorption of Light and Energy Conservation

In summary, the question is about energy conservation when an atom absorbs a photon and experiences changes in potential and kinetic energy. The expert explains that while the atom does recoil, the momentum of the photon is much smaller compared to the mass of the atom, similar to how the Earth does not recoil when hit by raindrops or even a larger comet.
  • #1
scienceteacher
8
0
Hello everybody. I apologize if this question is a little trivial compared to a lot of the threads posted, but I am an 8th grade science physical science teacher and am a little confused about some of the material.

From what I understand, if an atom absorbs a photon of energy E, then an electron will jump to a higher energy level. The change in potential energy that results from the EM field will be equal to the energy of the absorbed photon. All this I got from my understanding of spectral lines. Where I am confused is that I know the photon also has momemntum which must be conserved. If the photon transfers is momentum to the atom, the atom must have some Kinetic energy, which on a larger scal will translate to an increase in thermal energy. This seems to violate energy conservation. I know I must be missing something...what is it??

Thanks for the help Y'all!
 
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  • #2
scienceteacher said:
Hello everybody. I apologize if this question is a little trivial compared to a lot of the threads posted, but I am an 8th grade science physical science teacher and am a little confused about some of the material.

From what I understand, if an atom absorbs a photon of energy E, then an electron will jump to a higher energy level. The change in potential energy that results from the EM field will be equal to the energy of the absorbed photon. All this I got from my understanding of spectral lines. Where I am confused is that I know the photon also has momemntum which must be conserved. If the photon transfers is momentum to the atom, the atom must have some Kinetic energy, which on a larger scal will translate to an increase in thermal energy. This seems to violate energy conservation. I know I must be missing something...what is it??

Thanks for the help Y'all!

The atom does "recoil". However, you need to compare the momentum of a "typical" photon that is involved in such absorption versus the mass of the atom. For example, you don't see the Earth recoiling when raindrops hit its surface, do you? Even a larger comet hitting the Earth doesn't cause it to recoil much.

Zz.
 
  • #3


Hello, as a scientist, I would like to clarify and provide a response to your confusion about the absorption of light and energy conservation. You are correct in understanding that when an atom absorbs a photon of energy, an electron will jump to a higher energy level. This change in potential energy is equal to the energy of the absorbed photon, as you mentioned. However, when it comes to the momentum of the photon, it is important to note that momentum is not always conserved in the same way as energy. In the case of an atom absorbing a photon, the momentum of the photon is transferred to the atom, but it does not necessarily result in an increase in thermal energy. This is because the atom is already in motion due to its thermal energy, and the transferred momentum from the photon simply adds to its existing motion. Therefore, energy conservation is still upheld in this scenario. I hope this clarifies your confusion and helps in your teaching of physical science.
 

1. What is absorption of light?

Absorption of light is the process by which light energy is taken in and converted into another form of energy, such as heat or electrical energy. This occurs when light waves are absorbed by particles or molecules, causing them to vibrate and release energy.

2. How does absorption of light relate to energy conservation?

The absorption of light is an important part of energy conservation. When light is absorbed, it is not lost, but rather converted into a different form of energy. This process helps to maintain the overall balance of energy in a system.

3. What factors affect the absorption of light?

The absorption of light is affected by several factors, including the type of material the light is passing through, the wavelength of the light, and the intensity of the light. Different materials have different levels of transparency and absorb different wavelengths of light at different rates.

4. How does the color of an object relate to its absorption of light?

The color of an object is determined by the wavelengths of light it reflects and absorbs. Objects that appear black absorb almost all wavelengths of light, while objects that appear white reflect most wavelengths. The color of an object can also impact its ability to absorb light, as certain colors may absorb certain wavelengths more than others.

5. What are some real-life examples of absorption of light?

Absorption of light occurs in various real-life scenarios. Some common examples include plants absorbing light during photosynthesis, solar panels absorbing sunlight to convert into electricity, and the absorption of light by the Earth's atmosphere, which helps to regulate the Earth's temperature. Additionally, the color of clothing can affect how much light is absorbed by the fabric, impacting its ability to keep the wearer warm or cool.

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