Topic 6 - Waves

• White


  An object will appear white if it emits all wavelengths equally.
• 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).
• 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.
• Visible Light


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


  Used in energy efficient lamps and for sun tanning.
• Ultrasound Waves


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


  Waves with oscillations that are perpendicular to the direction of travel/energy transfer.
• Specular Reflection


  Reflection from a smooth surface, in a single direction.
• Sound Waves


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


  Waves that are produced by earthquakes.
• S-Waves


  Transverse, seismic waves that cannot travel through liquids.
• Reflection


  Reflection is when a wave bounces off a boundary. The angle of incidence always equals the angle of reflection.
• Radio Waves


  Used for television and radio signals. They can be produced by oscillations in electrical circuits.
• Radiation Dose


  A measure of the risk of harm to the body as a result of radiation exposure.
• Period


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


  An object that absorbs all radiation incident on it and does not reflect or transmit any type of radiation.
• P-Waves


  Longitudinal, seismic waves that travel at different speeds through solids and liquids.
• Normal


  The normal is an imaginary reference line that is constructed perpendicular to a boundary at the point that the wave intercepts it.
• Microwaves


  Used for satellite communications and for cooking food.
• Magnification


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


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


  An object that forms an image through the refraction of light.
• Ionising Radiation


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

  Used for cooking food, electrical heaters and infrared imaging.
• Infared 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.
• Human Hearing


  Humans can hear sounds in the frequency range of 20Hz to 20kHz.
• Hertz


  The unit of frequency.
• Frequency


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


  The distance between the centre of a lens and its principal focus.
• 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.
• Echo Sounding


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

  Reflection from a rough surface that results in scattering.
• Convex Lens


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


  A body remains at a constant temperature if it is absorbing radiation at the same rate that it is emitting it.
• Colour


  Colour is determined by frequency and wavelength.
• Colour Filters

  Filters that absorb certain wavelengths (colours) and transmit others. A blue filter for example will absorb all wavelengths other than those in the blue region of the colour spectrum.
• Black


  An object will appear black if it absorbs all wavelengths of radiation incident on it.
• Angle of Reflection


  The angle between the reflected ray and normal.
• Angle of Incidence


  The angle between the incident ray and normal.