Short Answer:

Drift velocity is the average velocity with which free electrons move through a conductor when an electric field is applied. Although electrons move randomly in all directions, the electric field causes a slight net movement in one direction, and this slow, overall motion is called drift velocity.

Drift velocity is very small, but it is important because it is responsible for electric current in metals. It depends on factors like the strength of the electric field, the type of material, and the number of free electrons available in the conductor.

Detailed Explanation:

Drift velocity

Drift velocity is a key concept in understanding how electric current flows in a conductor. In a metal conductor, electrons are always moving randomly due to thermal energy. When no electric field is applied, these random motions cancel out, and there is no net current. However, when a voltage is applied across the conductor, an electric field is created. This field exerts a force on the free electrons, slightly altering their paths and causing a slow net movement in the opposite direction of the electric field. This slow average motion is known as drift velocity.

Even though the individual electrons move at high speeds due to random motion, their net movement in one direction (drift) is very slow, usually just a few millimeters per second. Yet, this small movement is what causes electric current to flow in a wire.

Formula for drift velocity

The drift velocity vdv_dvd​ is given by the formula:

vd=InAev_d = \frac{I}{nAe}vd​=nAeI​

Where:

• vdv_dvd​ = drift velocity (in meters per second, m/s)
• III = electric current (in amperes)
• nnn = number of free electrons per unit volume (in electrons/m³)
• AAA = cross-sectional area of the conductor (in m²)
• eee = charge of an electron (1.6×10−191.6 \times 10^{-19}1.6×10−19 coulombs)

This formula shows that drift velocity is directly proportional to the current and inversely proportional to the number of electrons and the area of the conductor.

Key points about drift velocity

1. Very small in value:
   Even for large currents, the drift velocity is only a few millimeters per second.
2. Direction:
   Drift velocity is in the opposite direction of the electric field because electrons are negatively charged.
3. Relation with current:
   Drift velocity increases with current. Higher current means electrons drift faster.
4. Material dependent:
   Conductors with more free electrons (like copper and silver) have lower drift velocities for the same current.
5. Supports Ohm’s Law:
   Drift velocity helps explain how voltage, current, and resistance are related in a conductor.

Real-life importance

Even though electrons move slowly, electric signals travel quickly because the electric field affects all electrons in the wire almost instantly. This is why lights turn on immediately when you flip a switch, even though the drift velocity is very low.

Drift velocity is also useful in designing conductors and understanding how much current can safely flow through a wire. It helps engineers choose the right size and material of wires in electrical circuits.

Conclusion:

Drift velocity is the average slow speed at which free electrons move through a conductor under the influence of an electric field. Although it is very small, it is the actual motion responsible for electric current. It depends on the material, the amount of current, and the cross-sectional area of the wire. Understanding drift velocity is essential for analyzing current flow in electrical systems.