Name: Potentiometer & Rheostat
Uploaded: 2019-07-19
Duration: 7 min 9 s
Description: From audio to motion control, variable resistors have a wide range of applications. Here we introduce the working principle of variable resistors: Potentiome...

Question

Define drift velocity. Deduce the relation between drift velocity and current.

Accepted Answer

Subatomic particles like electrons move in random directions all the time. When electrons are subjected to an electric field they do move randomly, but they slowly drift in one direction, in the direction of the electric field applied. The net velocity at which these electrons drift is known as drift velocity.

Drift velocity can be defined as: The average velocity attained by charged particles, (e.g. electrons) in a material due to an electric field.

A material which allows current to pass through it is known as a conductor. No conductor will be perfect. It will have some resistance. The property to hinder the flow of current is called resistance and a device which does that is known as a resistor.

When charge is under motion current is produced. Here conductor connected to a potential difference will cause electrons to flow. Now rate of flow of these electrons is considered as magnitude of current which will be $‘ i ’$

Let us assume total number of electrons flowing per unit volume be $‘ n ’$ Charge of an electron be $‘ e ’$ Neglecting negative sign as we need only magnitude.

Magnitude of total electron charge would be $q = nV$

$q = e (nAx)$

$\frac{dq}{dt} = \frac{de (nAx)}{dt}$

$\frac{dq}{dt} = Ane \frac{dx}{dt} ∴ i = vAne$

Where $‘ V ’$ is volume which will be the product of area $(A)$ and displacement $(x)$ . cross section area $‘ A ’$ is constant but displacement $‘ x ’$ is varying. Rate of change of displacement is called drift velocity $(v) .$

Define drift velocity. Deduce the relation between drift velocity and current.

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