Detailed Notes - Current Electricity
Class 12 Physics | NCERT + Boards + JEE Main & Advanced
These notes are designed for complete chapter preparation. The PDF includes theory, derivations, formulas, NCERT
concepts, board-important points, JEE-level concepts, and PYQs.
1. Electric Current
•Electric current is defined as the rate of flow of electric charge through a conductor.
•Formula: I = Q/t
•SI Unit: Ampere (A)
•1 Ampere means 1 Coulomb charge flows per second.
•Conventional current flows from positive to negative terminal while electrons move in opposite direction.
•Current can exist only when there is a potential difference across the conductor.
2. Drift Velocity
•Free electrons move randomly inside a conductor.
•When electric field is applied, electrons acquire a small average velocity called drift velocity.
•Drift velocity is directly proportional to electric field.
•Important Formula: I = nAevd
•Where n = number density, A = area, e = charge of electron, vd = drift velocity.
•Relation: vd = eEτ/m
3. Ohm's Law
•At constant temperature, current through a conductor is directly proportional to applied voltage.
•Formula: V = IR
•Resistance is the opposition offered by conductor to current flow.
•Ohmic conductors follow straight line V-I graph.
•Non-ohmic conductors do not follow Ohm’s law.
4. Resistance and Resistivity
•Resistance depends on length, area and material of conductor.
•Formula: R = ρL/A
•Resistivity is an intrinsic property of material.
•Unit of resistivity = ohm-meter.
•Conductors have low resistivity while insulators have very high resistivity.
