1 Electric Current Ohm_s Law

Electric Current Ohm’s Law

Electric Current (I)

• It is the rate of flow of electric charge flowing though any section of wire.

• Unit of current is Ampere (A).
• One ampere of current flows in a wire when one coulomb of charge flows through the wire in one second.

Electric Current in a Conductor

• The electrons in a conductor move due to thermal motion during which they collide with the fixed ions.
• The direction of its velocity after the collision is completely random. At a given time, there is no preferential direction for the velocities of the electrons. Therefore, there will be no net current.
• Electrons in a conductor move under the action of the electric field applied across its two ends.

Ohm’s Law

• Electric current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor; physical quantities such as temperature, mechanical strain, etc. remaining constant.   V∝ I

V − I graph for an ohmic conductor

V = RI

Where, R is resistance of the conductor

• SI unit of resistance is ohm.
• Resistance of a conductor depends on:
• Length of the conductor (l)
• Area of cross-section (A) of the conductor

ρ is the electrical resistivity of the conductor.

• Using Ohm’s law,

is current per unit area, also called current density (J).

Let E be applied electric field across the conductor.

∴V = E l ……. (iii)

From equations (i), (ii), and (iii),

El = Jρl

E = Jρ

Where, is called the conductivity (σ)