CBSE · Class 12 · Physics · Current ElectricityState Ohm's Law and explain the physical significance of electrical resistance. Also, mention the factors on which the resistance of a conductor depends.

Ohm's Law states that at a constant physical temperature and mechanical state, the electric current ($I$) flowing through a conductor is directly proportional to the potential difference ($V$) applied across its ends. Mathematically, it is expressed as $V = IR$, where $R$ is a constant of proportionality known as the electrical resistance of the conductor. \nThe physical significance of resistance is that it represents the opposition offered by the material of the conductor to the flow of electric charges. Inside a conductor, free electrons collide repeatedly with fixed positive ions; these collisions impede their orderly drift, resulting in resistance. Due to this resistance, electrical energy is dissipated in the form of heat. \nThe electrical resistance of a uniform conductor depends on four primary factors:

1. Length ($l$): The resistance is directly proportional to the length of the conductor ($R \propto l$). Doubling the length doubles the resistance.
2. Cross-sectional Area ($A$): The resistance is inversely proportional to the cross-sectional area of the conductor ($R \propto 1/A$). A thicker wire offers less resistance.
3. Nature of the Material: Resistance depends heavily on the atomic structure and free electron density of the specific material being used (represented by resistivity, $\rho$).
4. Temperature: For metallic conductors, resistance increases linearly with a rise in temperature because thermal agitation increases the frequency of atomic collisions.