Question

Mobility is the drift velocity per unit

• A. charge
• B. volume
• C. electric field
• D. current
• E. time

Hint:

Mobility tells how easily charge carriers move under an electric field: \(\mu = v_d/E\).

Answer 1

The Correct Option is C

Step 1: Recall the definition of mobility.
Mobility (\(\mu\)) is defined as the drift velocity per unit electric field:
\[ \mu = \frac{v_d}{E} \]

Step 2: Identify each term.
Here, \[ v_d = \text{drift velocity}, \quad E = \text{electric field} \]

Step 3: Rearrange the formula.
\[ v_d = \mu E \] This shows that drift velocity is directly proportional to electric field.

Step 4: Interpret physically.
Higher electric field causes charge carriers to move faster, hence increases drift velocity.

Step 5: Check units.
\[ \mu = \frac{\text{m/s}}{\text{V/m}} = \text{m}^2/\text{V·s} \] which confirms the relation.

Step 6: Compare with options.
Mobility is clearly drift velocity per unit electric field.

Step 7: Final answer.
\[ \boxed{\text{electric field}} \] which matches option \((3)\).