Edexcel A-Level Physics Topic 5: Waves Definitions

Waves and the Particle Nature of Light

Amplitude

The maximum displacement from the rest position

Speed

Rate of coverage of distance

Period

Time taken to complete 1 cycle

Frequency

Number of waves (emitted from a source/passing a point) per second

Wavelength

Distance between adjacent points that are at the same point of the cycle (in phase)

Power

The amount of energy arriving (in joules) per second

Intensity

Amount of energy arriving (in joules) per second on each 1m² of area

Plane polarised electromagnetic wave

The oscillations of the electric field are all in the same plane (perpendicular to the direction of energy transfer)

Progressive wave

A wave where energy propagates outwards from it’s source

Transverse

Oscillations are perpendicular to the direction of energy transfer

Longitudinal

Oscillations are parallel to the direction of energy transfer

Compression

A point of high pressure on a longitudinal wave

Rarefaction

A point of low pressure on a longitudinal wave

Standing wave

Resultant superposition of two waves that are travelling in opposite directions and meeting. Waves have the same frequency and roughly the same attitude

Node

A point on a standing wave with minimum amplitude

Antinode

A point on a standing wave with maximum amplitude

Medium

Substance that the wave is propating through

Refractive index

Ratio of speed of light in a vacuum, to the speed of the wave in the medium

Refraction

The change of speed and direction of a wave when entering another medium

Total internal reflection

The whole wave is reflected at a boundary between two mediums. Occurs when travelling from a more optically dense medium to a less optically dense medium

Critical angle

The angle of incidence where the angle of refraction is 90 degrees

Superposition

The resultant displacement of a wave produced b the vector addition of the individual displacements of the meeting waves

Fundamental

Simplest mode of vibration

1st Harmonic

Simplest mode of vibration occuring at the lowest resonant frequency

Phase

The point in a cycle that a wave is - described as fractions of a wavelength, degrees or radians.

Phase difference

The difference between the points that 2 waves are in a cycle - in fractions of a wavelength, degrees or radians.

Focal point

Where rays from an object at infinity are brought into focus

Focal length

DIstance between the focal point and the plane of refraction / centre of the lens

Real image

The image can be projected onto a screen. The rays pass through the image.

Virtual image

An image that can’t be projected onto a screen. The image is formed where the rays appear to have originated from.

Upright image

The image has the same orientation as the object

Inverted image

If the object is upright, the image is upside down

Wavefront

A line joining all the points of a wave that are in phase with eachother

Coherent

Two waves with a consant phase relationship

Path difference

The difference in the distance travelled by 2 waves, expressed as a number of wavelengths

Interference

The resulting superposition from meeting waves

Constructive interference

The waves that meet and superimpose produce a resultant wavewith a greater amplitude than the individual waves

Destructive interference

The waves that meet and superpose produce a resultant wave with a smaller amplitude than the individual waves

Diffraction

A wave spreading out when passing through a gap that is comparable in size to the wavelength of the wave

Huygen’s construction

Imaginng that a wavefront is made up of point sources. Using the superposition of the circular wavefronts produced by these point sources, to predict the next wavefront

Photon

A discrete packet of energy (of an electromagnetic wave)

Photoelectric effect

Emitting an electron from the surface of a metal by radiating the metal surface with electromagnetic radiation

Threshold frequency

The minimum frequency of the incident electromagnetic radiation that can cause the emission of an electron from the surface of a metal

Work function

The minimum energ of the photons incident upon a metal surface required to cause the emission of an electron from the surface of a metal

Electronvolt

The amount of kinetic energy gained by an electron when accelerated through +1 volt.

Discrete energy levels

Electrons only being allowed in certain orbits around a nucleus