# Electrical mobility definition confusion

• Wminus
In summary, electrical mobility is defined as the ratio between the magnitude of the drift velocity and the magnitude of the electric field. Wikipedia may not be a rigorous source, but according to the definition, the velocity will always be parallel to the electric field regardless of the charge. However, in semiconductors, the mobility can be negative for electrons. In Kittel's reference book, the values of mobility are given as positive for both electrons and holes.
Wminus
Hi! According to this http://en.wikipedia.org/wiki/Electrical_mobility, the definition of electrical mobility ##\mu## is:

##\vec{v} = \mu \vec{E}##. But since electrical mobility is always positive, this means that the velocity is always parallel to the E-field regardless of charge. How can this be?

thanks for all replies.

Actually its not necessarily always positive. It can be negative in semiconductors.

Wikipedia is not a very rigorous source. It is good to get the idea of something and should not be taken too seriously. The mobility is defined as
v = +uE for 'holes.' And v = -uE for 'electrons.' Where v and E are vector quantities

Wminus said:
Hi! According to this http://en.wikipedia.org/wiki/Electrical_mobility, the definition of electrical mobility ##\mu## is:

##\vec{v} = \mu \vec{E}##. But since electrical mobility is always positive, this means that the velocity is always parallel to the E-field regardless of charge. How can this be?

thanks for all replies.
In the Wiki article they don't use vectors. The text explicitly mention that E is the magnitude of the electric field. So it is a scalar relation between the magnitudes of the drift velocity and of the electric field.
And this is how mobility is defined in Kittel's reference book: as ratio between magnitudes. The values of mobility are given as positive for both electrons and holes.

Wminus
Thanks guys

I apologise I should have been more specific that the minus sign cancels due to the relative direction of $$\vec v \ and\ \vec E$$]

## 1. What is electrical mobility?

Electrical mobility refers to the ability of charged particles, such as electrons and ions, to move through a medium in response to an electric field.

## 2. How is electrical mobility different from electrical conductivity?

Electrical mobility is a measure of how easily charged particles can move through a medium, while electrical conductivity is a measure of how well a material can conduct electricity.

## 3. What causes confusion in the definition of electrical mobility?

The confusion in the definition of electrical mobility often arises due to the use of different units and measurement methods, as well as the varying behavior of different types of charged particles.

## 4. What are the factors that affect electrical mobility?

The main factors that affect electrical mobility include the electric field strength, the properties of the medium (such as temperature and composition), and the properties of the charged particles themselves (such as mass and charge).

## 5. Why is understanding electrical mobility important in scientific research?

Electrical mobility plays a crucial role in various fields of research, such as atmospheric science, materials science, and biophysics. It helps scientists understand the behavior of charged particles in different environments and design more efficient processes and technologies.

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