Electrons, Waves & Photons Definitions: OCR AS Physics A

A collection of all of the important definitions, taken from all of the available past papers and also a few from textbooks

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Electrons, Waves & Photons
A continuous spectrum
All wavelengths/frequencies are present
A coulomb
One coulomb is the charge which passes a point when a current of 1A
flows for 1 second
A semi-conductor diode
Allows current in one direction only - A light-emitting diode (LED) emits light
when it conducts
Absorption line spectra
Spectra observed when white light is passed through a hot gas
Maximum displacement from the equilibrium position
A point of maximum amplitude along a stationary wave caused by
constructive interference.
Charge = Current x Time
Coherent light source
Source(s) have the same phase difference/ frequency/ wavelength/ amplitude
A flow of charge, in metals it is carried by electrons, in liquids it is carried by
free ions. Unit for charge is the coulomb; the unit for current is Cs-1, or

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De Broglie wavelength
Shows electrons behaving as waves, depending on speed/momentum
The spreading out of waves when they pass through a gap/edge of an object
Electromotive force
The energy transferred/gained per unit charge
A unit of energy - The amount of energy transferred when an electron moves
through a PD of 1 volt. 1eV = 1.…read more

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Longitudinal wave
Longitudinal waves have vibrations parallel to the direction in which the wave
Malus' law
Calculation for the intensity of light transmitted through a polarising filter:
Iout=Iin cos2
Mean drift velocity
Average distance travelled by electrons in the wire per second.…read more

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A quantum of energy
Plane polarisation
A process of restricting the vibrations of electromagnetic radiation to a single
Potential difference
The energy transferred/dissipated per unit charge
Rate of energy transfer. In electrical terms, power is the product of voltage
and current.…read more

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The Volt
A joule per coulomb
Component which shows a rapid change in resistance over a narrow
temperature range.…read more


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