Class 12 Physics: Current Electricity Vocabulary

Vocabulary and key concepts from Class 12 Physics Chapter 3 on Current Electricity, covering Ohm's Law, drift velocity, resistivity, and bridge circuits.

Electric Current ($I$)

The rate at which charge flows through a cross-sectional area, defined as $I = \frac{q}{t}$ for steady current and $I = \frac{dQ}{dt}$ for non-steady current.

Ampere ($A$)

The SI unit of electric current.

Ohm’s Law

A law stating that the potential difference $V$ across a conductor is directly proportional to the current $I$ flowing through it, expressed as $V = IR$.

Resistance ($R$)

The constant of proportionality in Ohm's Law that depends on the material and dimensions of the conductor, calculated as $R = \rho\frac{l}{A}$.

Resistivity ($\rho$)

A material-specific property that relates the resistance of a conductor to its length and area; metals have low values while insulators have values up to 18 orders of magnitude higher.

Current Density ($j$)

The current per unit area, defined as $j = \frac{I}{A}$, which is also proportional to the applied electric field ($$j = ext{σ} E$).

Conductivity ($\text{σ}$)

The reciprocal of resistivity ($\text{σ} = \frac{1}{\rho}$), indicating how easily current flows through a material; also expressed as $\text{σ} = \frac{ne^2\tau}{m}$.

Drift Velocity ($v_d$)

The average constant velocity attained by electrons due to an electric field despite collisions with ions, given by $v_d = \frac{eE\tau}{m}$.

Relaxation Time ($\tau$)

The average time interval between successive collisions of an electron with ions in a conductor.

Mobility ($\text{μ}$)

The magnitude of the drift velocity per unit electric field ($\text{μ} = \frac{|v_d|}{E}$), always a positive value.

Temperature Coefficient of Resistivity ($\text{α}$)

A constant that determines how the resistivity of a material changes with temperature in the relation $\rho = \rho_0[1 + \text{α}(T - T_0)]$.

Ohmic Loss

The heat generated in a resistor due to the flow of electric current ($I^2R$), serving as the basis for appliances like electric bulbs and heaters.

Electrical Power ($P$)

The rate of energy dissipation in a conductor, given by $P = IV$, $P = I^2R$, or $P = \frac{V^2}{R}$.

Electromotive Force (EMF, $\text{ε}$)

The potential difference between the positive and negative terminals of a cell when no current is flowing through the circuit.

Internal Resistance ($r$)

The inherent opposition to current flow within a cell, leading to a terminal voltage $V = \text{ε} - Ir$.

Wheatstone Bridge

An electrical circuit consisting of four resistors ($R_1$, $R_2$, $R_3$, $R_4$) used to measure an unknown resistance by achieving a balanced condition where the galvanometer current is zero ($I_g = 0$).

Balanced Bridge Condition

The specific state of a Wheatstone bridge where the ratio of resistances satisfies $\frac{R_1}{R_2} = \frac{R_3}{R_4}$, indicating no current flows through the galvanometer.

Meter Bridge

A practical measurement device that utilizes the Wheatstone bridge principle to determine unknown resistances via a balanced condition.