# Why High frequancy cause high resistance

1. Jan 3, 2008

### dumty

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.

2. Jan 3, 2008

### Manchot

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. Jan 3, 2008

### pixel01

I have read at high frequencies, a metal wire only conducts electricity on the surface, that's why the resistance increases.

4. Mar 24, 2010

### superflex

http://en.wikipedia.org/wiki/Skin_effect" [Broken]

Last edited by a moderator: May 4, 2017