Question

What is the SI unit of drift velocity?

Answer 1

The SI unit of **drift velocity** is **meters per second** (m/s).

### Explanation:
Drift velocity refers to the average velocity of charge carriers (such as electrons) in a conducting material when subjected to an electric field. It is the net velocity that the carriers acquire in the direction of the applied electric field.

- **Drift velocity (v_d)** is expressed mathematically as:

  \[
  v_d = \frac{I}{n A e}
  \]

  Where:
  - \( v_d \) is the drift velocity (in meters per second, m/s).
  - \( I \) is the current (in amperes, A).
  - \( n \) is the number of charge carriers per unit volume (in charges per cubic meter, \( \text{m}^{-3} \)).
  - \( A \) is the cross-sectional area of the conductor (in square meters, m²).
  - \( e \) is the charge of an electron (in coulombs, C).

### SI Unit Breakdown:
- **Current (I)** is measured in amperes (A), which is defined as coulombs per second (C/s).
- **Charge carrier density (n)** has units of \( \text{m}^{-3} \), or per cubic meter.
- **Cross-sectional area (A)** is measured in square meters (m²).
- **Elementary charge (e)** is measured in coulombs (C).

When considering these relationships, the drift velocity ends up with units of meters per second (m/s), as it represents the velocity of charge carriers in the material.

Answer 2

The drift velocity is the average velocity of charged particles (typically electrons) in a conductor when subjected to an electric field. It is a key concept in understanding electric current and the behavior of charge carriers in materials.

### SI Unit of Drift Velocity:

The drift velocity is a speed or velocity, so its SI (International System of Units) unit is the **meter per second (m/s)**.

### Detailed Explanation:

1. **Velocity and Units**:
   - Velocity, in general, measures the rate of change of displacement of an object. The SI unit of velocity is meters per second (m/s).
   - Drift velocity is a specific type of velocity, referring to the average velocity of charge carriers (like electrons) in a conductor, which move due to the applied electric field.

2. **Context of Drift Velocity**:
   - When a conductor (like a wire) is connected to a voltage source, an electric field is established within the conductor. This field exerts a force on the free charge carriers (usually electrons), causing them to accelerate in the direction opposite to the electric field.
   - In a real conductor, however, the electrons frequently collide with the atoms or impurities in the material, which hinders their motion and causes them to reach a constant average velocity known as the drift velocity.
   - The drift velocity depends on factors such as the magnitude of the electric field, the material's properties, temperature, and the density of charge carriers.

### Formula for Drift Velocity:

The drift velocity (\( v_d \)) can be calculated using the formula:

\[
v_d = \frac{I}{n A e}
\]

Where:
- \( v_d \) = Drift velocity (m/s)
- \( I \) = Electric current (amperes, A)
- \( n \) = Number of charge carriers per unit volume (m\(^{-3}\))
- \( A \) = Cross-sectional area of the conductor (m\(^2\))
- \( e \) = Elementary charge (Coulombs, C)

From the formula, it’s clear that drift velocity depends on current, the number of charge carriers, the area of the conductor, and the charge of each carrier.

In summary, drift velocity is the average speed of charge carriers due to the electric field in a conductor, and its SI unit is **meters per second (m/s)**, which aligns with the standard unit of velocity in physics.