Waves - Key Terms

• Transverse


  a wave in which the oscillations are at right-angles to the direction of energy transfer, e.g. water waves
• Longitudinal


  a wave in which the oscillations are parallel to the direction of energy transfer, e.g. sound waves
• Oscillate

  to vibrate / swing from side to side with a regular frequency
• Frequency


  the number of times that a wave / vibration repeats itself in a specified time period
• Amplitude

  the maximum displacement that any particle in a wave achieves from its undisturbed position, measured in metres (m)
• Wavelength


  the distance from one point on a wave to the equivalent point on the next wave, measured in metres (m), represented by the symbol λ
• Period


  the time taken for a wave to complete one oscillation; the time it takes for a particle in the wave to move backwards and forwards once around its undisturbed position
• Medium

  a material or substance
• Reflected


  when a wave meets a boundary between two different materials and is bounced back
• Refracted


  when a wave meets a boundary between two different materials and changes direction
• Absorbed


  to take in and retain (all or some) incident radiated energy
• Transmitted


  when waves are sent out from a source or pass through a materia
• Normal


  at right-angles to / perpendicular to
• Refractive index


  a measure of the extent to which light is refracted by a material
• Ultrasonic


  sound waves with a frequency greater than 20kHz, so they cannot be heard by humans
• Echo sounding


  to determine depth by measuring the time taken for a pulse of high-frequency sound to reach the sea bed or a submerged object and for the echo to return
• Seismic


  caused by an earthquake
• P-waves

  (Primary waves) the longitudinal seismic waves produced during an earthquake
• S-waves

  (Secondary waves) the transverse seismic waves produced during an earthquake
• Electromagnetic (EM) waves

  a continuous spectrum of waves formed by electric and magnetic fields, ranging from high frequency gamma rays to low frequency radio waves
• Microwaves


  electromagnetic radiation in the wavelength range 0.3 to 0.001 metres, used in satellite communication and cooking
• Infared


  the part of the electromagnetic spectrum with a longer wavelength than light but a shorter wavelength than radio waves
• Ultraviolet


  the part of the electromagnetic spectrum with wavelengths shorter than light but longer than X-rays
• X-rays


  the part of the electromagnetic spectrum with wavelengths shorter than that of ultraviolet radiation but longer than gamma rays
• Gamma


  high frequency, short wavelength electromagnetic waves; a type of nuclear radiation, emitted from a nucleus
• Ionising


  refers to radiation that can cause atoms to lose or gain atoms, becoming ions
• Convex


  having one or two surfaces curved outwards; a convex lens is sometimes called a converging lens because parallel rays of light entering the lens are brought to a focus
• Concave


  having one or two surfaces curved inwards; a concave lens is sometimes called a diverging lens because parallel rays of light entering the lens spread out
• Principal focus


  (also called focal point) the point where parallel rays of light travelling through a lens converge (meet) or from which they appear to diverge (spread out) from refraction by the lens
• Focal length


  the distance from the centre point of a lens to the focus point, where the light rays converge / come together
• Real


  refers to an image produced by a lens, which is on the opposite side of the lens to the object and can be projected onto a screen (opposed to a virtual image)
• Virtual


  refers to an image produced by a lens, which is on the same side of the lens as the object and can only be seen by looking through the lens (opposed to a real image)
• Principal axis


  the horizontal line that runs straight through the centre of a lens
• Magnification

  the ratio of image height to object height, e.g. magnification = image height / object height
• Specular reflection


  reflection in a single direction (no scattering of light)
• Transparent


  an object that transmits light coherently (the light rays do not get scattered), so that objects on the other side can be seen clearly
• Translucent


  an object that transmits light, but scatters the rays so that objects cannot be seen clearly through it
• Opaque


  describes an object that either reflects or absorbs all light incident on its surface, so that no light passes through it
• Emit

  to give off (radiation or particles)
• Absorb

  to take in and retain (all or some) incident radiated energy