Current Electricity – Key Vocabulary

These flashcards cover essential vocabulary from the lecture notes on Current Electricity, including fundamental quantities, laws, material properties, circuit rules, and measurement techniques.

Electric Current (I)

Net charge that crosses a given area per unit time; measured in amperes (A).

SI unit of electric current; one coulomb per second.

Ampere

Current Density (j)

Current per unit cross-sectional area normal to flow (A m⁻²).

Drift Velocity (v_d)

Average velocity with which charge carriers move under an electric field inside a conductor.

Relaxation Time (τ)

Average time interval between successive collisions of charge carriers with lattice ions.

Mobility (μ)

Magnitude of drift velocity per unit electric field (m² V⁻¹ s⁻¹).

Electric Field (E)

Force per unit charge; inside a conductor relates to current density by j = σE.

Ohm’s Law

For many conductors V ∝ I, expressed as V = RI where R is constant.

Resistance (R)

Ratio of voltage across a conductor to current through it; measured in ohms (Ω).

Ohm (Ω)

SI unit of resistance; one volt per ampere.

Resistivity (ρ)

Material property given by ρ = RA/l; measured in Ω m.

Conductivity (σ)

Reciprocal of resistivity; σ = 1/ρ (S m⁻¹).

Temperature Coefficient of Resistivity (α)

Fractional change in resistivity per unit temperature rise for a material.

Conductor

Material with low resistivity (~10⁻⁸–10⁻⁶ Ω m) allowing easy flow of current.

Insulator

Material with extremely high resistivity, restricting electric current.

Semiconductor

Material whose resistivity lies between conductors and insulators and decreases with temperature.

Internal Resistance (r)

Resistance offered by the electrolyte and electrodes within a cell.

Electromotive Force (emf, ε)

Open-circuit potential difference between cell terminals; work done per unit charge by the source.

Terminal Voltage

Potential difference across cell terminals under load; V = ε − Ir.

Ohmic Loss (I²R loss)

Electrical power converted into heat in a resistor; P = I²R = V²/R.

Series Combination of Cells

Cells connected end-to-end; εeq = Σεi and req = Σri.

Parallel Combination of Cells

Cells with like terminals connected together; 1/req = Σ(1/ri) and εeq/req = Σ(εi/ri).

Kirchhoff’s Junction Rule

Sum of currents entering a junction equals sum leaving; based on charge conservation.

Kirchhoff’s Loop Rule

Algebraic sum of potential changes around any closed circuit loop is zero.

Wheatstone Bridge

Four-resistor network used to measure unknown resistance; balanced when R₁/R₂ = R₃/R₄.

Meter Bridge

Practical Wheatstone bridge using a uniform resistance wire to measure an unknown resistance.

Battery Arm

Diagonal in Wheatstone bridge across which the emf source is connected.

Galvanometer Arm

Diagonal in Wheatstone bridge containing the galvanometer to detect bridge balance.

Current Source

Device (cell or battery) that maintains electric current in a circuit by doing work on charges.

Charge Carrier

Particle (electron or ion) whose motion constitutes electric current.

Drift Current

Component of current arising from drift velocity under applied electric field.

Random Thermal Motion

Erratic movement of electrons in absence of field, yielding zero net current.

Power (P)

Rate at which electrical energy is supplied or dissipated; P = IV.

Resistive Heating

Conversion of electrical energy into heat due to resistance; basis of electric heaters.

Balance Condition (Bridge)

State when galvanometer current is zero; ensures accurate resistance measurement.

Maximum Current of Cell

Limit I_max = ε/r when external resistance is zero.

Drift Equation

Relation j = n e v_d, linking current density with carrier density and drift speed.

Conduction Electron

Nearly free electron in a metal responsible for electrical conductivity.

Mobility Formula

μ = eτ/m, showing mobility depends on relaxation time and carrier charge-to-mass ratio.

Temperature Dependence (Metals)

Resistivity increases linearly with temperature over modest ranges: ρT = ρ0[1 + α(T − T_0)].