Waves and Particle Nature of Light

Flashcards for review of lecture notes about Waves and Particle Nature of Light.

Amplitude

A wave’s maximum displacement from the equilibrium position.

Frequency (f)

The number of complete oscillations passing through a point per second.

Period (T)

The time taken for one full oscillation.

Speed (v)

The distance travelled by the wave per unit time.

Wavelength (λ)

The length of one whole oscillation (e.g. the distance between successive peaks/troughs).

Wave equation

The speed (v) of a wave is equal to the wave’s frequency multiplied by its wavelength.

Longitudinal waves

In longitudinal waves, the oscillation of particles is parallel to the direction of energy transfer.

Rarefaction

Neighbouring particles move away from each other

Compression

Neighbouring particles move towards a point

Transverse waves

In transverse waves, the oscillations of particles (or fields) is at right angles to the direction of energy transfer.

Coherence

A coherent light source has the same frequency and wavelength and a fixed phase difference.

Wavefront

A wavefront is a surface which is used to represent the points of a wave which have the same phase.

Constructive interference

This occurs when two waves are in phase and so their displacements are added

Destructive interference

This occurs when the waves are completely out of phase and so their displacements are subtracted

Waves in phase

Two waves are in phase if they are both at the same point of the wave cycle, meaning they have the same frequency and wavelength (are coherent) and their phase difference is an integer multiple of 360° (2π radians).

Waves out of phase

Two waves are completely out of phase when they have the same frequency and wavelength (are coherent) and their phase difference is an odd integer multiple of 180° (π radians).

Stationary waves

A stationary wave (also known as a standing wave) is formed from the superposition of 2 progressive waves, travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude.

Antinodes

Regions of maximum displacement in a stationary wave.

Nodes

Regions of no displacement in a stationary wave.

Intensity

Power (energy transferred per unit time) per unit area.

Refractive index (n)

A property of a material which measures how much it slows down light passing through it.

Refraction

Occurs when a wave enters a different medium, causing it to change direction, either towards or away from the normal depending on the material’s refractive index.

Critical angle (C)

When the angle of refraction is exactly 90° and the light is refracted along the boundary, the angle of incidence has reached this.

Total internal reflection (TIR)

Occurs when the angle of incidence is greater than the critical angle and the incident refractive index (n1) is greater than the refractive index of the material at the boundary (n2).

Plane polarisation

A polarised wave oscillates in only one plane.

Diffraction

The spreading out of waves when they pass through or around a gap.

Huygens’ construction

Every point on a wavefront is a point source to secondary wavelets, which spread out to form the next wavefront

Diffraction grating

A slide containing many equally spaced slits very close together.

Zero order line

The ray of light passing through the centre of a diffraction grating

de Broglie hypothesis

States that all particles have a wave nature and a particle nature, and that the wavelength of any particle can be found using the following equation: λ = p h

Interface

A boundary between two materials.

Pulse-echo technique

Used with ultrasound waves (sounds waves with a frequency greater than 20 kHz) for the imagining of objects, notably for medical imaging.

Photon model

EM waves travel in discrete packets called photons, which have an energy directly proportional to their frequency.

Photoelectricity

Where photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.

Threshold frequency

The minimum frequency of light required to emit photoelectrons, and this varies depending on the type of metal.

Work function

The minimum energy required for electrons to be emitted from the surface of a metal

Electronvolt (eV)

A unit of energy, usually used to express small energies.

Atomic line spectra

Says electrons in atoms can only exist in discrete energy levels.