Physics
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Drift Velocity Calculator.
Calculate charge-carrier drift speed from current, carrier density, charge, and area.
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01
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02 / ANSWER
Drift velocity: 0.000073 m/s
Results update automatically as you type.
Use Cases
Physics Education
Helps students and educators understand the relationship between current, carrier density, and drift velocity in conductors.
Example: Calculate the drift velocity of electrons in a copper wire with a given current and cross-sectional area.
Electrical Engineering Design
Assists engineers in estimating carrier speeds in conductive materials to evaluate performance and safety.
Example: Determine if drift velocity in a power cable is within expected limits for a given load.
Frequently Asked Questions
- What is drift velocity?
- Drift velocity is the average speed at which charge carriers, such as electrons, move through a conductor when an electric field is applied. It is typically very slow, on the order of millimeters per second, despite the fast propagation of the electric field.
- How is drift velocity calculated?
- Drift velocity (v) is calculated using the formula v = I / (n * q * A), where I is the current in amperes, n is the carrier number density in m⁻³, q is the charge magnitude in coulombs, and A is the conductor's cross-sectional area in m².
- What units are used in this calculator?
- The calculator uses SI units: current in amperes (A), carrier number density in m⁻³, charge magnitude in coulombs (C), and conductor area in square meters (m²). The resulting drift velocity is in meters per second (m/s).
Tips & Common Mistakes
Tips
- Ensure carrier number density is in m⁻³; for copper, it's approximately 8.5 × 10²⁸ m⁻³.
- Use consistent units: convert area to m² if given in mm² or cm².
- Remember that drift velocity is an average; individual electrons move randomly at much higher speeds.
- For semiconductors, carrier density can vary with doping; use the appropriate value for your material.
Common Mistakes to Avoid
- Forgetting to convert area from mm² to m² (1 mm² = 1 × 10⁻⁶ m²).
- Using the charge of an electron (1.6 × 10⁻¹⁹ C) but not accounting for the sign; this calculator uses magnitude.
- Confusing carrier number density with mass density; they are different properties.
Last updated: August 13, 2026