Physics Definitions (Module 4)

Coulomb

Coulomb

One coulomb of charge passes a point in one second when there is an electric current of one ampere flowing

Ampere

The current flowing in two parallel wires in a vacuum one metre apart such that there is an attractive force of 2.0 × 10^-7N per metre length of wire between them

Electric current

The rate of flow of charged particles

Conventional current

A model used to describe the net movement of charge in a circuit. Conventional current travels from the positive terminal (longer line) to the negative terminal (shorter line)

Conservation of charge

Charge is conserved in all interactions: it cannot be created or destroyed

Kirchhoff’s first law

The sum of the currents entering any point in an electrical circuit is always equal to the sum of the currents leaving that point, as charge is conserved

Electrolyte

A fluid that contains ions that are free to move and, therefore, conduct electricity

Progressive wave

A transfer of energy as a result of the oscillations of the medium or particles through which the energy is travelling

Longitudinal wave

A wave whereby the oscillations of the particles of the medium are parallel to the direction of travel

Transverse wave

A wave whereby the oscillations of the particles of the medium are perpendicular to the direction of travel

Displacement (waves)

The distance of a point on the wave from the equilibrium position

Amplitude (waves)

The maximum displacement of any point on the wave from the equilibrium position

Wavelength (waves)

The distance from any point on the wave to the next subsequent point in phase

Wave speed (waves)

The speed at which energy is transmitted by the wave

Frequency (waves)

The number of oscillations at a point per unit time

Period (waves)

The time taken for one complete oscillation

Phase difference

How far “out of step” the oscillations at two points on the same wave are

Diffraction

The spreading out of a wave after passing through a gap or past an obstacle

Plane polarised wave

A wave with oscillations in one plane only, which is normal to the direction of propagation

Intensity

The rate of energy incident per unit area at right angles to the direction of propagation

Interference

When two or more coherent waves superpose at a point, there is a change in overall displacement

Principle of superposition

When two waves interfere at a point, the resultant displacement is the sum of the individual displacements

Path difference

The extra distance travelled by one of the waves compared with the other

Coherent sources

Sources of waves that have a constant phase difference

Node

A point where the amplitude of vibrations is always zero

Antinode

A point where the amplitude of vibrations always takes the maximum possible value

Photon

A quantum of energy of electromagnetic radiation

Electronvolt

The energy gained by an electron that is accelerated through a potential difference of one volt

Threshold frequency

The minimum frequency of radiation needed for electrons to be released from a metal surface during the photoelectric effect

Workfunction of a metal

The minimum energy required to eject an electron from a metal surface

Number density

The number of free (delocalised) electrons per metre cubed of a material

Conductor

A material with a high number density of conduction electrons and therefore, a low resistance

Semiconductor

A material with a lower number density of conduction electrons than a conductor and therefore, a higher resistance

Insulator

A material with a small number density of conduction electrons and therefore, a very high resistance

Mean drift velocity

The average displacement of electrons per unit time as they move along a wire

Electromotive force (EMF)

The energy transferred per unit charge when one type of energy is converted into electrical energy

Potential difference

The energy transferred per unit charge when electrical energy is converted into another form of energy

Volt

Two points in a circuit are at a potential difference of one volt if one joule of energy is transferred when one coulomb of charge passes from one point to the other

Resistance

The resistance of a conductor is the ratio of the potential difference across it to the current through it

Ohm

A conductor has a resistance of one ohm if there is a potential difference of one volt across it when there is a current of one ampere through it

Ohm’s law

For a metallic conductor at constant temperature, the current in the conductor is directly proportional to the potential difference across its ends

Resistivity

The product of the material’s resistance and its cross-sectional area per unit length

Kilowatt-hour

The energy dissipated by a 1.0kW electrical device in a time of one hour, which is equivalent to 3.6MJ

Kirchhoff’s second law

The sum of the EMFs around any closed loop in a circuit is equal to the sum of the PDs around the same closed loop

Internal resistance

Some energy is transformed into thermal energy within the cell; the cell behaves as if it had a resistance