Electric current (I = Q/t = neAvd) is the rate of flow of charge, driven by an electric field that propagates at nearly the speed of light, even though individual electrons drift at ~10^{-4} m/s.

Ohm's law (V = IR) applies to ohmic conductors at constant temperature; resistance R = ρl/A, where resistivity ρ is an intrinsic material property independent of shape.

For metals, resistance increases with temperature (α > 0) because higher temperatures reduce relaxation time τ; for semiconductors, resistance decreases (α < 0) because carrier concentration n increases exponentially.

Resistors in series share the same current (R_eq = ΣRᵢ); resistors in parallel share the same voltage (1/R_eq = Σ(1/Rᵢ)); these rules are exactly opposite to capacitor combination rules.

Power dissipation P = VI = $I^{2}$R = $V^{2}$/R; for parallel resistors on the same battery, total power is $n^{2}$ times larger than for the same resistors in series.

A real cell has EMF ε and internal resistance r; terminal voltage V = ε − Ir during discharge, meaning V is always less than ε when current flows.

Kirchhoff's current law (ΣI = 0 at junctions) and voltage law (Σ$\Delta V$ = 0 in loops) provide a complete framework for analyzing any linear circuit, based on conservation of charge and energy respectively.

A Wheatstone bridge is balanced when P/Q = R/S, giving zero galvanometer current; the metre bridge is a practical version using a uniform 1-metre wire with formula R/S = l/(100 − l).

The potentiometer measures true EMF (not terminal voltage) because at the null point no current flows from the test cell, eliminating the internal Ir voltage drop.

NEET focuses on: drift velocity dependence, bridge balance calculations (including arm interchange), potentiometer EMF comparison and internal resistance, power ratio in series vs parallel, and the sign of temperature coefficient for metals versus semiconductors.