The mobility of charge carriers in a conductor is given by the expression: drift velocity/electric field.

Explanation:
1. Mobility of charge carriers:
- The mobility of charge carriers refers to the ability of charge carriers (such as electrons) to move through a material when an electric field is applied.
- It is a measure of how easily charge carriers can move in response to an electric field.

2. Drift velocity:
- When an electric field is applied to a conductor, it exerts a force on the charge carriers, causing them to move.
- The average velocity at which charge carriers move in response to the electric field is called the drift velocity.
- Drift velocity is generally very small, on the order of millimeters per second.

3. Electric field:
- An electric field is created by applying a potential difference (voltage) across the conductor.
- The electric field exerts a force on the charge carriers, causing them to move.

4. Relationship between mobility, drift velocity, and electric field:
- The mobility of charge carriers is defined as the ratio of their drift velocity to the electric field applied.
- Mathematically, mobility (μ) = drift velocity (v_d) / electric field (E).
- The unit of mobility is meters per second per volt per meter (m^2/Vs).

5. Significance of mobility:
- Mobility is an important parameter in understanding the behavior of charge carriers in a material.
- It helps in characterizing the conductivity of a material and predicting its electrical properties.
- Materials with higher mobility of charge carriers tend to have better conductivity.

In summary, the mobility of charge carriers in a conductor is given by the expression drift velocity/electric field. This expression represents the ratio of the average velocity of charge carriers (drift velocity) to the electric field applied. Mobility is an important parameter in understanding the behavior of charge carriers in a material and characterizing its conductivity.