# Why Do Metals Stop Reflecting Light at Certain Frequencies?

• DariusP
In summary, the conversation discusses the concept of plasma frequency and its relationship to metals. The question posed is why metals reflect light and why their reflectivity drops at a certain frequency, which is known as the plasma frequency. It is explained that metals have a metallic bond and can be analyzed like plasma due to an equal distribution of electrons and positively charged atoms. The conversation also mentions that metals are good at reflecting light, but at a certain frequency, their reflectivity decreases rapidly.
DariusP
Hello, I am having a very hard time understanding what is plasma frequency by reading definitions. I know, for example, that metals have a metallic bond and can be analysed like plasma because of an equal distribution of electrons in electron gas and positively charged atoms.

I know metals are very good at reflecting light but at certain frequency their reflectivity drops very fast and this frequency where the drop happens is, I think, what's called - plasma frequency.

The question: Why do metals reflect light and why at certain frequency they stop reflecting?

There is a description in the following video which is quite easy to follow:-

## 1. What is plasma frequency?

Plasma frequency is the resonant frequency at which a plasma oscillates when subjected to an electric field. It is a characteristic property of a plasma and is determined by its density and the charge of its constituent particles.

## 2. How is plasma frequency calculated?

The plasma frequency can be calculated using the formula ωp = √(nq^2/ε0m), where ωp is the plasma frequency, n is the plasma density, q is the charge of the particles, ε0 is the permittivity of free space, and m is the mass of the particles.

## 3. What is the significance of plasma frequency?

The plasma frequency is significant because it determines the behavior of a plasma when subjected to an external electric field. It also plays a role in determining the optical and electrical properties of a plasma.

## 4. How does plasma frequency differ from plasma resonance frequency?

Plasma frequency and plasma resonance frequency are often used interchangeably, but they are not exactly the same. Plasma resonance frequency is the frequency at which plasma absorbs the maximum amount of energy, while plasma frequency is the frequency at which plasma oscillates when subjected to an electric field.

## 5. What factors affect the plasma frequency?

The plasma frequency is affected by the density and charge of the particles in the plasma, as well as the temperature and magnetic field. It also depends on the type of particles present in the plasma, such as electrons, ions, or both.

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