Waves

  • Created by: AMcL1
  • Created on: 28-05-19 14:50

Properties of Waves

  • Transverse Wave - A vibration causing the wave to be at right angles to the direction of energy transfer (side to side). The energy is carried outwards by the wave. These include examples of water, light and secondary waves.
  • Longitudinal Waves - A vibration causing the wave to be parallel to the direction of energy transfer (back and forth). The energy is carried along the wave. These include examples of sound and primary waves.
  • Measuring Speed - In water, measure the speed of waves in a ripple tank, and in air, use echoes.
  • Period - The time taken to produce one complete wave.
  • Frequency - The number of waves per second.
  • Amplitude - The maximum disturbance of the wave from its rest position.
  • Wavelength - The disance from one point on a wave to the same point on the next wave.
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Light

  • Reflection - Where the wave bounces off of the surface.
  • Refraction - Where waves change direction at a boundary.
  • Transmitted - When a wave passes through the object.
  • Absorbed - Where the wave passes into but not out of an object, transferring energy to it and causing it to heat up.
  • Light refracts as it slows down in a denser substance.
  • Angle of incidence (i) = Angle of reflection (r)
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Sound

  • Hearing - Between the frequencies of 20 and 20,000 Hz, longitudinal waves cause the ear drum to vibrate. These vibrations are amplified by three ossicles which creates pressure in the cochlea. This is how we hear sound. Below 20Hz and over 20,000Hz the frequencies are out of the range of the human ear.
  • When sound waves travel through different mediums, the frequency always stays constant.
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Waves in the World Today

  • Seismic Waves - These are produced by earthquakes. Primary seismic waves are longitudinal, fast and they travel through solids and liquids. Secondary seismic waves are transverse, slow and they only travel through solids. Seismographs are used to show the primary and secondary waves arriving at different times. By using the times that the waves arrive at the monitoring centres, the epicentre of the earthquake can be found.
  • Ultrasound - These waves are partially reflected off of the boundary and are used for medical and foetal scans.
  • Sonar - These waves are reflected off of objects and are used to determine the depth of objecst under the sea.
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Electromagnetic Spectrum - Part 1

  • Electromagnetic Wave Spectrum - The continuous spectrum of tranverse waves. Short wavelengths have a high frequency and high energy (e.g gamma). 
  • Absorbed light changes into thermal energy stores. Different types can be seen below.
  • Black Surfaces - These are good emitters and good absorbers.
  • White Surfaces - These are poor emitters and poor absorbers.
  • Shiny Surfaces - These are good reflectors.
  • The waves at the beginning of the elctromagnetic spectrum have a low frequency and a long wavelength, meaning they have less energy. In comparison, the waves towards the end of the elcetromagnetic spectrum have a high frequency and a short wavelength, meaning that they have more energy.
  • Electromagnetic waves refract.
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Electromagnetic Spectrum - Part 2

  • Radio - These are safe and are used for communications, TV and radio.
  • Microwave - These can burn if they are concentrated, and are used in mobile phones, cooking and satellites.
  • Infrared - These can also burn if they are concentrated and are used in heating, remote controls and cooking.
  • Visible Light - These can cause damage to eyes and are used for illumination, photography and fibre optics.
  • Ultraviolet - These can cause sunburn and cancer, but are used in security marking and disinfecting water.
  • X-Ray - These can cause cell destruction, mutation and cancer. They are used to detect broken bones and also in airport security.
  • Gamma - These can also cause cell destruction, mutation and cancer, and are used for sterilising and detecting and killing cancer.
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Lenses

  • Image Size = Actual Object Size x Magnification (I=AM)
  • Convex Lens - Can show real or virtual images.
  • Concave Lens - Can only show virtual images.
  • 2F = Image is the same size, upside down and real.
  • 2F - F = Image is larger, upside down and real.
  • < F = Image is bigger, the right way and virtual.
  • Specular - This is flat surface reflection.
  • Diffuse - This is rough surface reflection.
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Black Body Radiation

  • Black Body Radiation - This is where all objects absorb or reflect infrared radiation. Objects that are hotter emit more infrared radiation. 
  • Constant Temperature - This is where the rate of absorption is equal to the rate of radiation. Both the intensity and wavelength of energy affects the temperature.
  • Earth and Global Warming - Ultraviolet, visble light and infrared radiation penetrate the atmosphere and heat up the earth's surface. From here, the longer wavelengths are radiated back, trapped by the atmosphere. This means that the rate of energy lost is not the same as the rate of energy being absorbed and so the earth heats up.
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Equations and Units

  • Wave Speed = Frequency x Wavelength (V = f x lamda)
  • Wave Period = 1 / Frequency (T = 1 / f)
  • Speed = Distance / Time (V = d / t)
  • Distance - Metres (m)
  • Wave Speed - Metres per Second (m/s)
  • Wavelength - Metres (m)
  • Frequency - Hertz (Hz)
  • Period - Seconds (s)
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