Mobility
The magnitude of the drift velocity per unit electric field, representing the ease with which charge carriers move in a material.
What is Mobility?
The magnitude of the drift velocity of charge carriers per unit applied electric field.
Key formula / rule: Mobility
Key points
- Define mobility and state its SI unit.
- Explain the relationship between mobility, drift velocity, and electric field.
- Understand how mobility affects the conductivity of a material.
- Identify factors that influence mobility.
Common exam trap
Confusing mobility with drift velocity or current density.
Definitions
- Term
Mobility
- Meaning
The magnitude of the drift velocity of charge carriers per unit applied electric field.
- Term
Drift Velocity
- Meaning
The average velocity attained by charge carriers in a material due to an applied electric field.
Learning objectives
Define mobility and state its SI unit.
Explain the relationship between mobility, drift velocity, and electric field.
Understand how mobility affects the conductivity of a material.
Identify factors that influence mobility.
Formulae
- Name
Mobility
- Note
μ is mobility, |vd| is the magnitude of drift velocity, E is the electric field strength.
- Expression
\μ = \frac{|vd|}{E}
- Name
Conductivity in terms of Mobility
- Note
σ is conductivity, n is the number of charge carriers per unit volume, q is the charge of each carrier.
- Expression
\σ = nq\μ
Prerequisites
Electric Field
Drift Velocity
Electric Current
Charge Carriers
Common mistakes
Confusing mobility with drift velocity or current density.
Assuming mobility is constant for all materials or under all conditions.
Forgetting the units of mobility.
Not understanding the inverse relationship between mobility and scattering events.
Keywords
Mobility
Drift Velocity
Electric Field
Charge Carriers
Conductivity
Semiconductor Physics
Electrical Conduction
Practice preview
What is the SI unit of mobility of charge carriers in a conductor?…
easy
If the drift velocity of electrons in a conductor is 2.5 x 10^-4 m/s when an electric field of 100 V/m is applied, what is the mobility of the electrons?…
medium
Which of the following quantities represents the ease with which charge carriers move in a material under the influence of an electric field?…
easy