OCR • J259 • 108 key terms
Absolute zero
A temperature of –273°C (0 K), the lowest possible temperature, above which all objects constantly emit and absorb electromagnetic radiation.
From: Climate change and evidence
Absorber
A material or object that takes in electromagnetic radiation, converting its energy into other forms.
From: Properties of the Electromagnetic Spectrum
Absorption
The process where the energy of a wave is taken in by the particles of a material.
From: Transmission, Absorption and Colour
Albedo
A measure of the reflectivity of a surface, determining how much incoming radiation is reflected rather than absorbed.
From: Climate change and evidence
Alternating current (AC)
An electric current that periodically reverses direction and changes its magnitude continuously with time.
From: Uses and Hazards of Electromagnetic Waves
Amplitude
The maximum displacement of a point on a wave away from its undisturbed (rest) position.
From: The Wave Equation and Measuring Wave Speed
Analogue signal
A signal that can vary continuously in amplitude and frequency.
From: Uses and Hazards of Electromagnetic Waves
Angle of deviation
The angle between the original path of an incident white light ray and the path of the emergent coloured ray after passing through a prism.
From: Reflection, Refraction and Lenses
Angle of incidence
The angle measured between the incoming incident ray and the normal.
From: Reflection, Refraction and Lenses
Angle of reflection
The angle measured between the outgoing reflected ray and the normal.
From: Reflection, Refraction and Lenses
Angle of refraction
The angle measured between the refracted ray and the normal inside the new medium.
From: Reflection, Refraction and Lenses
Black body
An idealized object that perfectly absorbs all incident electromagnetic radiation and acts as the most effective possible emitter.
From: Climate change and evidence
Cataracts
A clouding of the lens in the eye, the risk of which is significantly increased by exposure to ultraviolet radiation.
From: Uses and Hazards of Electromagnetic Waves
Compressions
Regions in a longitudinal wave where the particles are close together at high pressure.
From: Properties and Types of Waves
Concave lens
A lens that is thinner in the middle and causes parallel rays of light to diverge.
From: Reflection, Refraction and Lenses
Convex lens
A lens that is thicker in the middle and causes parallel rays of light to converge at a principal focus.
From: Reflection, Refraction and Lenses
De-excitation
The process of an electron falling back to a lower energy level, releasing energy as a photon of EM radiation.
From: Atomic Interactions and Generation of Radiation
Differential absorption
The selective taking-in of specific wavelengths of light by a substance while reflecting or transmitting others.
From: Transmission, Absorption and Colour
Diffract
The spreading out of waves as they pass through a gap or around an obstacle.
From: Uses and Hazards of Electromagnetic Waves
Diffuse reflection
Reflection from a rough surface where parallel light rays are scattered in different directions.
From: Reflection, Refraction and Lenses
Digital signal
A signal that has only two possible states: on (1) or off (0).
From: Uses and Hazards of Electromagnetic Waves
Dispersion
The splitting of white light into its constituent colours due to the different speeds (and therefore different refraction angles) of each colour in a medium.
From: Reflection, Refraction and Lenses
Displacement
The distance a part of the wave medium has moved from its rest position at any given moment.
From: Properties and Types of Waves
Echo
A reflected sound wave.
From: The Wave Equation and Measuring Wave Speed
Electromagnetic (EM) radiation
Energy transferred through space by transverse waves, which includes visible light, ultraviolet, and infrared.
From: Climate change and evidence
Electromagnetic (EM) spectrum
A continuous range of frequencies of electromagnetic radiation, grouped into seven main regions.
From: Properties of the Electromagnetic Spectrum
Electromagnetic spectrum
The continuous range of electromagnetic waves arranged by frequency or wavelength.
From: Properties and Types of Waves
Electromagnetic wave
A transverse wave that can travel through a vacuum at the speed of light and does not require a medium.
From: Properties and Types of Waves
Electron transitions
The movement of electrons between different energy levels within an atom.
From: Atomic Interactions and Generation of Radiation
Emission
The process by which an object gives out electromagnetic radiation, transferring thermal energy away from itself.
From: Climate change and evidence
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