Current Electricity Lecture Flashcards

This set of vocabulary flashcards covers fundamental concepts of current electricity, including charge, potential, resistance, Ohm's law, and commercial energy units, based on the provided lecture transcript.

Positive charge

The condition of a body which loses electrons during the rubbing of two non-conducting bodies.

Negative charge

The condition of a body which gains electrons during the rubbing of two non-conducting bodies.

Coulomb ($C$)

The S.I. unit of charge, where the charge on an electron is $-1.6 \times 10^{-19}\,C$.

Electric Current ($I$)

The rate of flow of charge, defined as the amount of charge flowing per second across any cross section of a conductor ($I = \frac{Q}{t}$).

Ampere ($A$)

The S.I. unit of current, defined as one coulomb of charge passing through a conductor in one second.

Ammeter

An instrument used to measure current in a circuit by connecting it in series.

Electric Potential ($V$)

The amount of work done per unit charge in bringing a positive test charge from infinity to a specific point ($V = \frac{W}{Q}$).

Volt ($V$)

The S.I. unit of electric potential and potential difference, equal to one joule per coulomb ($1\,V = 1\,J\,C^{-1}$).

Potential Difference (p.d.)

The work done per unit charge in moving a positive test charge from one point to another point in an electric circuit.

Voltmeter

An instrument used to measure potential difference, connected in parallel across the points of interest in a circuit.

Resistance ($R$)

The obstruction offered to the flow of current by a conductor or wire.

Ohm ($\Omega$)

The S.I. unit of resistance, where one ohm is the resistance when $1\,A$ of current flows under a potential difference of $1\,V$.

Ohm's Law

The law stating that current flowing in a conductor is directly proportional to the potential difference across its ends, provided temperature and physical conditions remain constant ($V = IR$).

Conductance ($G$)

The reciprocal of resistance, with the unit siemen (symbol $S$) or $\Omega^{-1}$.

Ohmic resistors

Conductors that obey Ohm's Law, such as silver, copper, and nichrome, where the $V$-$I$ graph is a straight line passing through the origin.

Non-ohmic resistors

Conductors that do not obey Ohm's Law, such as LEDs, solar cells, and junction diodes, where the $V$-$I$ graph is a curve.

Specific Resistance (Resistivity) ($\rho$)

A characteristic property of a material defined as the resistance of a wire of unit length and unit area of cross section ($\rho = \frac{Ra}{l}$).

Conductivity ($\sigma$)

The reciprocal of specific resistance, measured in $\Omega^{-1}\,m^{-1}$ or siemen metre$^{-1}$.

Superconductor

A substance that has zero resistance (or infinite conductance) at very low temperatures near absolute zero, such as mercury below $4.2\,K$.

Electro-motive force (e.m.f.) ($\varepsilon$)

The work done per unit charge in taking a positive test charge around the complete circuit, including inside the electrolyte and the external circuit.

Terminal Voltage ($V$)

The potential difference between the electrodes of a cell when current is being drawn (closed circuit).

Voltage Drop ($v$)

The work done per unit charge in carrying a positive test charge through the electrolyte inside the cell, given by $v = Ir$.

Internal Resistance ($r$)

The resistance offered by the electrolyte inside the cell to the flow of current.

Electrical Power ($P$)

The rate at which electrical energy is supplied by a source, calculated as $P = VI = I^2R = \frac{V^2}{R}$.

Watt ($W$)

The S.I. unit of electrical power, consumed when a current of $1\,A$ flows through a circuit with a potential difference of $1\,V$.

Kilowatt-hour ($kWh$)

The commercial unit of electrical energy, equal to $3.6 \times 10^6\,J$, consumed by a $1\,kW$ appliance in one hour.

Joule's Law of Heating

The principle stating that the heat produced ($H$) in a wire is directly proportional to the square of the current ($I^2$), the resistance ($R$), and the time ($t$).