G482 Difinitions Flashcards
Compressions
A region in a longitudinal wave (e.g sound wave) where te particles are closest together.
Amplitude of wave
Maximum displacement.
Displacement
The distance of an oscillating particle measured from the mean/equilibrium/undisturbed position (expressed as a vector).
Frequency
The number if complete wavelengths passing a point per unit time.
Intensity
Intensity is the (incident) energy per unit (cross-sectional) area per second.
Longitudinal wave
A wave where the oscillations/vibrations of the particles/medium are in the direction of travel of the wave. E.g. Sound
Mechanical wave
A wave which requires particles/a medium in order to be able to travel. E.g. Sound & water
Phase
This is the stage that a particle has reached with complete oscillation. ???????????
Progressive wave
A wave which transfers energy/shape/information from one place to another.
Rarefaction
A region in a longitudinal wave ( such as a sound wave) where the particles are furthest apart.
Reflection
When a wave hits a surface and bounces back.
Refraction
When a wave crosses an interface between two medium and so changes its speed. If the wave hits the interface at an angle (not 90 degrees), then it changes direction.
Speed of wave
Distance travelled by the wave per unit time.
Time (period), T
Time taken for one complete oscillation of a particle. T=1/f
Transverse wave
A wave where the oscillation/vibration of the particles/medium (in the plane) are at right angle to the direction of travel of the wave. E.g. Surface water waves or electromagnetic waves.
Wave
A periodic disturbance which carried energy as it travels. It is characterised by vibrations (oscillations) of the particles/medium (or fields for electromagnetic waves only).
Wavefront
A set of particles which are all in phase and the same direction from the source.
Wavelength
The distance between two neighbouring identical points which are at the same phase.
Continous spectrum
The electromagnetic spectrum where all wavelength/frequencies are present (in the radiation).
Dispersion
The splitting of light into its different wavelengths (to make a spectrum).
Electromagnetic waves (electromagnetic spectrum)
A family of waves which are made from oscillating electric and magnetic fields. All the waves are transverse and can travel through a vacuum at the speed if light, c = 3.0 X 10*8 ms-1
Malus’s Law
The intensity if light transmitted through a polarising filter is equal to I0cos*2 0
Plane polarisation
Where the oscillations if the electric field are in one plane only. Only transverse waves can be polarised.
Typical wavelength values for light and UV waves
Visible 600-400nm
UV-A 400-315nm
UV-B 315-260nm
UV-C 260-100nm
Vacuum
A region where there are no particles.
Coherence
There is a constant phase difference between 2 waves.
Constructive interference
The interference of two or more coherent waves which are in phase, resulting in their mutual reinforcement (the path difference between two such waves is nXwavelength.
Destructive interference
The interference of two or more coherent waves which are in antiphase, resulting in their cancellation (the path difference between two such waves is (n+0.5).
Diffraction
The spreading if a wave as it passes through a gap or past the edge of an object.
Interference
Interference is when (two) waves meet/combine/interact/superpose (at a point) causing a change in overall intensity/displacement.
Path difference
The difference in the distance travelled by two waves from coherent sources, measured at a particular point.
Phase difference
The fraction of a cycle between the oscillations of two particles, measured in radians.
Superposition
When two waves combine, their displacement are added together like vectors.
Antinode
A point on a standing wave where the amplitude is always at its maximum possible value.
Difference between progressive waves and stationary waves
- Stationary waves store energy; progressive waves transfer energy.
- Stationary waves have nodes and antinodes; progressive wave do not.
Fundamental (frequency)
Simplest pattern of movement of standing wave which has the lowest possible frequency/longest wavelength.
Node separation
The separation between two adjacent nodes (or antinodes) which is equal to wavelength/2.
Node
A point on a standing wave where the amplitude is always zero.
Stationary (or standing) wave
A wave which stores rather than transferring energy; the shape does not move along. Formed when an incident wave is reflected and then interferes/superposes with the incident wave to produce (a resultant wave with) nodes and/or antinodes.
De Broglie wavelength
The wavelength of an electron which depends on its speed/momentum. It arises because electrons can behave as waves/show wavelike properties.
Electron diffraction
When electrons are fired at a sample (e.g. Graphite) and a resulting interference pattern can be observed. This shows that electrons can be diffracted, therefore they are behaving as waves.
Energy in eV
Energy in J = energy in eV X 1.6x10*-19
1J = 1.6x10*-19 eV
Photoelectric effect
When a photo is absorbed by an electron in a metal surface, causing an electron (with energy above the work function) to be emitted.
(Einstein’s) Photoelectric equation
Energy of incoming photon = work function X energy of emitted photoelectron
Photon
A quantum of energy of electromagnetic radiation.
Threshold frequency
The minimum frequency if electromagnetic radiation which will eject photoelectrons from the surface of a metal.
Work function
The minimum energy required to release an electron from the surface of a metal.
Absorption line spectrum
A series of dark lines (appearing against a bright background/within a continuous spectrum).
Emission line spectrum
Is formed by light emitted from (excited isolated) atoms in a low pressure gas. It produces a series of (sharp/bright/coloured) lines against a dark background.
Energy level
A quantised energy state of an orbital electron i. An atom.
Ground state
The lowest energy stare that can be occupied by an orbital electron in an atom.
Ionisation energy
The energy required to remove an orbital electron completely from its atom.
Transition
When an electron ‘jumps’ between two energy levels.
Electronvolt
The energy gained by an electron travelling through a p.d. of 1 volt.
1 eV = 1.6x10*-19
Kirchhoff’s first law
The sum of the current entering any point (or junction) in a circuit is equal to the sum of current leaving that same point. This law conveys the conservation of charge.
Kirchhoff’s second law
The sum of the e.m.f.s round a loop in a circuit is equal to the sum of p.d.s in that same loop.
