Current Electricity: Formulas, Laws, and Definitions

Vocabulary practice flashcards covering fundamental concepts, electrical laws, circuit elements, and equations in current electricity.

Temperature Coefficient of Resistance ($\alpha$)

The fractional change in electrical resistance of a conductor per unit rise in temperature, defined mathematically by $\alpha = \frac{R_\theta - R_0}{R_0\theta}$, where $R_\theta = R_0(1 + \alpha\theta)$.

Mechanical Equivalent of Heat ($J$)

The constant ratio of mechanical work ($W$) performed to the quantity of heat ($H$) produced, expressed by the relationship $J = \frac{W}{H}$.

Primary Cell

An electrochemical cell that continuously produces electric current using chemical energy and cannot be recharged once exhausted, such as a Leclanché cell or dry cell.

Secondary Cell

An electrochemical cell that produces electric current using chemical reactions and can be electrically recharged after discharge, such as a lead-acid accumulator cell.

Electromotive Force (EMF)

The total work done per unit electric charge in circulating it around an entire closed circuit, given by $E = \frac{W}{q}$ with the SI unit of volt ($\text{V}$).

Drift Velocity ($v$)

The average velocity acquired by free charge carriers (electrons) inside a conductor due to an applied electric field, related to electric current by $I = nAve$.

Current Density ($j$)

The electric current flowing per unit cross-sectional area of a conductor, defined as $j = \frac{I}{A} = nve$, with the SI unit of $\text{A}\,\text{m}^{-2}$.

Ohm's Law

The physical law stating that, at constant temperature, the current ($I$) through a conductor is directly proportional to the potential difference ($V$) across its ends, formulated as $I = \frac{V}{R}$.

Conductance ($G$)

A measure of how easily electric current passes through a conductor, defined as the reciprocal of electrical resistance ($G = \frac{1}{R}$).

Internal Resistance ($r$)

The inherent resistance offered by the electrolyte and electrodes of an electric cell to the flow of current within itself, leading to the relation $E = I(R + r)$.

Kirchhoff's Current Law (KCL)

The junction rule stating that the algebraic sum of all electric currents meeting at any circuit junction is zero ($\sum I = 0$), signifying that total incoming current equals total outgoing current.

Kirchhoff's Voltage Law (KVL)

The loop rule stating that in any closed circuit loop, the algebraic sum of the products of current and resistance equals the total electromotive force ($\sum IR = \sum E$).

Shunt

A low-resistance conductor connected in parallel with a galvanometer to protect it from excessive current and divide the circuit current.

Multiplying Factor of a Shunt

The ratio that determines the factor by which a galvanometer's measuring range is extended when equipped with a shunt ($S$), given by $\frac{G + S}{S}$.

Ammeter

An instrument connected in series in a circuit to directly measure current, constructed by connecting a low-resistance shunt ($S$) in parallel with a sensitive galvanometer coil.

Wheatstone Bridge

An electrical network of four resistors used to determine an unknown resistance, achieving a balanced condition where no current flows through the central galvanometer when $\frac{R_1}{R_2} = \frac{R_3}{R_4}$.

Meter Bridge

A practical apparatus based on the Wheatstone bridge principle used to measure an unknown resistance along a calibrated slide-wire, governed by $\frac{P}{Q} = \frac{100 - r}{r}$.

Potentiometer

An accurate electrical instrument used to compare the electromotive forces of cells or measure the internal resistance of a cell without drawing current at the null point.

Ampere-Hour ($\text{A}\cdot\text{h}$)

A unit of electric charge representing the total amount of charge transferred by a steady current of one ampere flowing continuously for a duration of one hour.