Why High frequancy cause high resistance

In summary, there is a mathematical equation known as the Drude Model that shows how resistance increases as frequency increases. This model assumes that electrons in a solid are free to move but are scattered by collisions, resulting in a decrease in conductivity at high frequencies. This can be observed in the skin effect, where a metal wire only conducts electricity on its surface at high frequencies.
  • #1
dumty
1
0
well i have a question in my mind.
is there any mathematical equation or law that shows how the resistance increases as we increase the Frequencies.
 
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  • #2
In fact, there is. One of the simplest models of conductivity is the Drude Model, which assumes that electrons in a solid move freely when an electric field is applied, but are scattered by collisions every so often (with an average lifetime called the scattering time). Surprisingly, it works pretty well for many materials. Wikipedia has a page on it which gives the differential equation and resultant conductivity equation.

Essentially, the conductivity doesn't change by very much at low frequencies, but for frequencies on the order of 1/(scattering time), it drops quickly. Physically, what this means is that for high frequency signals, electrons are getting scattered so quickly that they don't really have a chance to respond to the field.
 
  • #3
I have read at high frequencies, a metal wire only conducts electricity on the surface, that's why the resistance increases.
 
  • #4
http://en.wikipedia.org/wiki/Skin_effect"
 
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  • #5


Yes, there is a mathematical equation that shows how the resistance increases as we increase the frequency. This is known as the skin effect and it is described by the following equation:

R = (sqrt(π*f*μ/σ)) / (2*σ)

Where R is the resistance, f is the frequency, μ is the permeability of the material, and σ is the conductivity of the material. This equation shows that as the frequency increases, the resistance also increases due to the skin effect. This is because at higher frequencies, the current tends to flow more on the surface of the material, rather than through the entire cross-section. This increased surface current results in higher resistance. Additionally, at higher frequencies, the electrons in the material have less time to move, leading to a decrease in conductivity and an increase in resistance. Therefore, high frequency causes high resistance due to the skin effect and decreased conductivity.
 

1. Why does high frequency cause high resistance?

High frequency causes high resistance because the electrons in a conductor are not able to move freely as the frequency increases. As the frequency increases, the electrons are forced to change direction more frequently, leading to collisions and a decrease in their ability to flow through the material.

2. How does the frequency of an electrical current affect resistance?

The frequency of an electrical current directly affects resistance. As the frequency increases, the resistance also increases due to the decrease in electron mobility. This is known as the skin effect, where the current is forced to flow on the surface of the conductor rather than through its entire cross-section.

3. Is there a limit to the amount of resistance that can be caused by high frequency?

Yes, there is a limit to the amount of resistance that can be caused by high frequency. This is known as the skin depth, which is the depth at which the current density decreases by a factor of 1/e (about 37%). Beyond this depth, the resistance begins to decrease again as the current is able to flow more freely through the material.

4. Can high frequency resistance be reduced?

Yes, high frequency resistance can be reduced by using materials with high conductivity, such as copper or silver, which have a lower skin depth and therefore experience less resistance at high frequencies. Additionally, using thicker conductors can also decrease the overall resistance by increasing the skin depth and allowing for more current to flow through the material.

5. How does high frequency resistance affect electronic devices?

High frequency resistance can affect electronic devices in a variety of ways. It can cause overheating and damage to components, reduce the efficiency and reliability of circuits, and impact the overall performance of the device. It is important for electronic engineers to consider high frequency resistance when designing and testing electronic devices to ensure optimal functionality.

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