pmt definitions

• Amplitude


  The maximum displacement of a wave from its undisturbed (equilibrium) position
• Angle of Incidence


  The angle between the incident ray and normal
• Angle of Reflection


  The angle between the reflected ray and normal
• Black


  An object will appear black if it absorbs all wavelengths of radiation incident on it
• Colour Filters


  Filters that absorb certain wavelengths (colours) and transmit others
• Colour


  Colour is determined by frequency and wavelength
• A body remains at a constant temperature if it is absorbing radiation at the same rate that it is emitting it
• Convex Lens


  A lens that brings parallel rays to focus at the principal focus. The image formed can be either real or virtual
• Diffuse Reflection

  Reflection from a rough surface that results in scattering
• Echo Sounding

  A technique that uses high frequency sound waves to detect objects in deep water and to measure the depth of water
• Electromagnetic Waves


  Transverse waves that transfer energy from the source of the waves, to an absorber. They form a continuous spectrum of different frequencies and all travel at the same speed in a vacuum
• Focal Length


  The distance between the centre of a lens and its principal focus
• Frequency


  The number of waves passing a given point in a second. It is the inverse of the wave's period
• Hertz

  The unit of frequency
• Humans can hear sounds in the frequency range of 20Hz to 20kHz
• Infrared Radiation

  A type of radiation that all objects emit and absorb. The hotter an object is, the greater the infrared radiation it emits in a given time
• Infrared

  Used for cooking food, electrical heaters and infrared imaging
• Ionising Radiation


  Radiation that can cause the mutation of genes and cause cancer. X-rays and gamma rays are both forms of ionising radiation
• Lens

  An object that forms an image through the refraction of light
• Longitudinal Waves


  Waves with oscillations that are parallel to the direction of travel/energy transfer
• Magnification


  The ratio of the image height over the object height for a lens. Since it is a ratio, it has no units
• Microwaves


  Used for satellite communications and for cooking food
• Normal


  The normal is an imaginary reference line that is constructed perpendicular to a boundary at the point that the wave intercepts it
• 1. Waves are longitudinal, seismic waves that travel at different speeds through solids and liquids
• Perfect Black Body


  An object that absorbs all radiation incident on it and does not reflect or transmit any type of radiation
• Period


  The time it takes for one complete wave to pass a given point. It is the inverse of frequency
• Radiation Dose


  A measure of the risk of harm to the body as a result of radiation exposure
• Radio Waves


  Used for television and radio signals. They can be produced by oscillations in electrical circuits
• Reflection is when a wave bounces off a boundary. The angle of incidence always equals the angle of reflection
• 1. Waves are transverse, seismic waves that cannot travel through liquids
• Seismic Waves


  Waves that are produced by earthquakes
• Sound Waves


  The longitudinal waves responsible for sound. In solids, sound waves are transmitted by the vibrations of the solid's particles
• Specular Reflection


  Reflection from a smooth surface, in a single direction
• Transverse Waves


  Waves with oscillations that are perpendicular to the direction of travel/energy transfer
• Ultrasound Scanning


  A technique that involves ultrasound waves being transmitted and then partially reflected at a boundary before being detected by a detector. The time between transmission and detection can be used to calculate distances, and build up an image
• Ultrasound Waves


  Waves that have a frequency higher than the upper limit of human hearing (20kHz)
• Ultraviolet


  Used in energy efficient lamps and for sun tanning
• Visible Light


  The only type of electromagnetic radiation that our eyes can detect. It is used for fibre optic communications
• Wave Speed

  The speed at which energy is transferred through the medium. It is equal to the product of the wave's wavelength and frequency
• Wavelength

  The distance from a point on one wave to the same point on the adjacent wave (ie. peak to peak or trough to trough)