Δp for total reflection and absorbtion of E&M radiation explanation?

In summary, the equation for the change in momentum of electromagnetic radiation for total absorption is ΔU/c and for total reflection is (2ΔU)/c. This means that the momentum of electromagnetic radiation, which is massless and travels at a constant speed c, can either increase or decrease depending on whether it is absorbed or reflected. The ΔU represents a change in frequency of the radiation. The reason for the change in momentum being double for total reflection is similar to a ball hitting a wall and stopping versus rebounding with the same speed. This is because the momentum changes from +mv to -mv, resulting in a total change of 2mv.
  • #1
Phyzwizz
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The equation for the change in momentum for total absorption of electromagnetic radiation is ΔU/c and that for total reflection is (2ΔU)/c. How could the momentum of electromagnetic radiation change if it is massless and travels at a constant speed c? Is the ΔU just a representation of a change in the frequency of the radiation? Also my book does a poor job in explaining the reason that the change in momentum is double for total reflection (perhaps this will become more clear with an explanation of the previous questions).Δ
 
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  • #2
The change in momentum for reflection is 2 x thechange for absorption for the same reason that the change in momentum for a ball hitting a wall and stopping dead is mv but a ball rebounding with the same speed has a change in momentum of 2mv. Momentum changes from +mv to -mv.
 
  • #3
Complete Reflection

Δp = ΔU/c - (-ΔU/c) = 2(ΔU/c)
 

1. What is Δp for total reflection and absorption of E&M radiation?

Δp, also known as the momentum change, is a measure of the change in momentum of an electromagnetic (E&M) radiation particle when it interacts with a surface. This value is dependent on the angle of incidence and the properties of the material, and it can be used to explain the behavior of E&M radiation when it is reflected or absorbed.

2. How is Δp related to the total reflection and absorption of E&M radiation?

The value of Δp is directly related to the total reflection and absorption of E&M radiation. When the angle of incidence is small, the momentum change is also small, resulting in a high probability of reflection. On the other hand, when the angle of incidence is large, the momentum change is also large, leading to a higher chance of absorption. Essentially, Δp helps to determine the outcome of E&M radiation interacting with a surface.

3. What factors influence the value of Δp?

The value of Δp is influenced by several factors, including the angle of incidence, the properties of the material (such as refractive index and density), and the wavelength of the E&M radiation. These factors can affect the momentum change and ultimately determine the behavior of the E&M radiation when it interacts with a surface.

4. How does Δp explain the phenomenon of total internal reflection?

In the case of total internal reflection, the angle of incidence is greater than the critical angle, resulting in a momentum change that is too large for the E&M radiation to be transmitted through the material. This leads to a complete reflection of the radiation, as explained by the value of Δp. This phenomenon is commonly seen in materials with a high refractive index, such as glass or water.

5. Can Δp be used to predict the behavior of E&M radiation in all situations?

While Δp is a useful tool for explaining the total reflection and absorption of E&M radiation, it may not accurately predict the behavior in all situations. Other factors, such as the surface roughness and the presence of other materials, can also influence the outcome of E&M radiation interaction. Therefore, it is important to consider all relevant factors when studying the behavior of E&M radiation.

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