Question:

The magnitude of tfie drift velocity per unit electric field is defined as

Updated On: Apr 7, 2025

conductivity
resistivity
Mobility
current density
impedance

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The Correct Option is C

Approach Solution - 1

Drift Velocity and Mobility

We are asked to identify the term that defines the magnitude of the drift velocity per unit electric field.

Step 1: Define Drift Velocity

Drift velocity ($v_d$) is the average velocity that charge carriers (e.g., electrons in a metal) attain due to an electric field. It's the net velocity of the charge carriers in a particular direction.

Step 2: Define Mobility

Mobility ($\mu$) is defined as the drift velocity per unit electric field:

$\mu = \frac{|v_d|}{E}$

Where:

$\mu$ is the mobility.
$v_d$ is the magnitude of the drift velocity.
$E$ is the magnitude of the electric field.

Step 3: Why Conductivity is Incorrect

Conductivity ($\sigma$) is a measure of a material's ability to conduct electric current. It is related to the drift velocity and mobility, but it is not the *definition* of drift velocity per unit electric field. Conductivity is given by:

$\sigma = nq\mu$

Where:

$\sigma$ is the conductivity.
$n$ is the number density of charge carriers.
$q$ is the charge of the charge carrier.
$\mu$ is the mobility.

Conductivity depends on both mobility AND the density and charge of the carriers.

Conclusion

The magnitude of the drift velocity per unit electric field is defined as Mobility.

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