Mobility
Mobility is defined as the magnitude of the drift velocity per unit electric field, indicating how easily charge carriers move in a material.
What is Mobility?
The magnitude of the drift velocity acquired by charge carriers per unit applied electric field.
Key formula / rule: Mobility
Key points
- Define mobility.
- Explain the relationship between mobility, drift velocity, and electric field.
- Identify the SI unit of mobility.
- Understand the factors affecting mobility.
Common exam trap
Confusing mobility with drift velocity or electric field.
Definitions
- Term
Mobility (μ)
- Meaning
The magnitude of the drift velocity acquired by charge carriers per unit applied electric field.
- Term
Drift Velocity (vd)
- Meaning
The average velocity attained by charge carriers in a material due to an applied electric field.
- Term
Electric Field (E)
- Meaning
A region around a charged particle or object within which a force would be exerted on other charged particles or objects.
Learning objectives
Define mobility.
Explain the relationship between mobility, drift velocity, and electric field.
Identify the SI unit of mobility.
Understand the factors affecting mobility.
Relate mobility to conductivity.
Formulae
- Name
Mobility
- Note
μ is mobility, vd is drift velocity, E is electric field.
- Expression
\μ = \frac{vd}{E}
- Name
Conductivity in terms of mobility
- Note
σ is conductivity, n is charge carrier density, q is the charge of the carrier (e for electrons, +e for holes).
- Expression
\σ = nq\μ
Prerequisites
Electric Field
Drift Velocity
Conductors and Semiconductors
Charge Carriers
Common mistakes
Confusing mobility with drift velocity or electric field.
Forgetting the units of mobility.
Assuming mobility is constant for a given material under all conditions (it varies with temperature and impurities).
Keywords
Mobility
Drift Velocity
Electric Field
Charge Carriers
Conductivity
Semiconductors
Metals
Material Property
Practice preview
The mobility of charge carriers is a measure of:…
easy
A charge carrier in a material has a drift velocity of 5 x 10⁻⁴ m/s when subjected to an electric field of 2 x 10⁻² V/m. Calculate the mobility of the charge carrier.…
medium
Consider two materials, A and B. Material A has a mobility of 0.1 m²/(V·s) and material B has a mobility of 0.01 m²/(V·s). If both are subjected to the same electric field, which statement is correct?…
medium