Example
Let's say the current (I) is 5 A, the number of charge carriers (n) is \( 1 \times 10^{28} \) 1/m³, the charge of each carrier (q) is \( 1.6 \times 10^{-19} \) C, and the cross-sectional area (A) is \( 1 \times 10^{-6} \) m². Using the formula:
\[
v_d = \frac{5}{1 \times 10^{28} \cdot 1.6 \times 10^{-19} \cdot 1 \times 10^{-6}}
\]
We get:
\[
v_d = 3.125 \times 10^{-4} \, \text{m/s}
\]
So, the drift speed is approximately \( 3.125 \times 10^{-4} \) m/s.
Average Drift Speed Formula
Formula: \( v_d = \frac{I}{nAe} \)
- \( v_d \): Drift speed
- \( I \): Current
- \( n \): Number of charge carriers per unit volume
- \( A \): Cross-sectional area
- \( e \): Charge of an electron
Example: \( v_d = \frac{10}{5 \times 2 \times 1.6 \times 10^{-19}} \)
- Current (I): 10 A
- Number of charge carriers per unit volume (n): 5
- Cross-sectional area (A): 2 m²
- Charge of an electron (e): (1.6 \times 10^{-19}) C
Estimate the Average Drift Speed
Formula: \( v_d = \frac{I}{nAe} \)
- \( v_d \): Drift speed
- \( I \): Current
- \( n \): Number of charge carriers per unit volume
- \( A \): Cross-sectional area
- \( e \): Charge of an electron
Example: \( v_d = \frac{15}{6 \times 3 \times 1.6 \times 10^{-19}} \)
- Current (I): 15 A
- Number of charge carriers per unit volume (n): 6
- Cross-sectional area (A): 3 m²
- Charge of an electron (e): (1.6 \times 10^{-19}) C
Drift Velocity Equation
Formula: \( v_d = \frac{I}{nAe} \)
- \( v_d \): Drift speed
- \( I \): Current
- \( n \): Number of charge carriers per unit volume
- \( A \): Cross-sectional area
- \( e \): Charge of an electron
Example: \( v_d = \frac{20}{4 \times 2.5 \times 1.6 \times 10^{-19}} \)
- Current (I): 20 A
- Number of charge carriers per unit volume (n): 4
- Cross-sectional area (A): 2.5 m²
- Charge of an electron (e): (1.6 \times 10^{-19}) C
