Wave properties

• Waves


  Transfer energy without transferring matter; particles oscillate about a fixed point
• Amplitude


  • The distance from the equilibrium position to the maximum displacement
• Wavelength


  • The distance between a point on one wave and the same point on the next wave

  
• Frequency


  • The number of waves that pass a single point per second

  
• Speed


  • The distance travelled by a wave each second
• Speed relationship


  1. Speed = Frequency x Wavelength

  2. v = f λ

  
• Transverse waves


  • Has peaks and troughs
  • Vibrations are at right angles to the direction of travel
  • Example: light

  
• Longitudinal waves


  • Consists of compressions and rarefactions
  • Vibrations are in the same direction as the direction of travel
  • Example: sound

  
• Wavefront


  A surface containing points affected in the same way by a wave at a given time such as crests or troughs

  
• Reflection


  • Waves reflect off smooth, plane surfaces rather than getting absorbed
  • Angle of incidence = angle of reflection
  • Rough surfaces scatter the light in all directions
  • Frequency, wavelength, and speed are all unchanged

  
• Refraction


  • The speed of a wave changes when it enters a new medium
  • If the wave enters a more optically dense medium, its speed decreases and it bends towards the normal
  • If the wave enters a less optically dense medium, its speed increases and it bends away from the normal
  • Frequency stays the same but the wavelength changes

  
• Diffraction


  • Waves spread out when they go around the sides of an obstacle or through a gap
  • The narrower the gap or the greater the wavelength, the more the diffraction
  • Frequency, wavelength, and speed are all unchanged

  
• Reflection of light


  • Upright
  • Same distance from the mirror as the object
  • Same size
  • Virtual

  
• Refractive index


  The ratio between the speed of light in a vacuum and the speed of light in the medium

  
• Snell's law


  n = sin i / sin r where i is the angle of incidence and r is the angle of refraction

  
• Total internal reflection


  • Occurs when the angle of incidence is greater than the critical angle and the light reflects back into the medium
  • Requires light to be travelling from a more optically dense medium into a less optically dense medium
  • Critical angle can be related to refractive index by n = 1/sin c

  
• Optical fibre


  A long thin rod of glass surrounded by cladding which uses total internal reflection to transfer information by light, even when bent

  
• Converging lens


  • Brings light rays together at a point called the principal focus by utilising refraction
  • The focal length is the distance between the centre of the lens and the principal focus
  • Can form real or virtual images

  
• Dispersion


  When white light is passed through a glass prism, it splits up into its constituent colours because the different colours travel at different speeds in the glass

  
• Electromagnetic spectrum


  • Radio waves
  • Microwaves
  • Infrared radiation
  • Visible light
  • Ultraviolet light
  • X-rays
  • Gamma radiation

  
• As wavelength decreases


  Frequency must increase
• Ionising radiation


  1. rays and gamma rays that can cause mutations leading to cancer
• Sound waves


  • Longitudinal waves created by vibrating sources
  • Require a medium to transmit
• Amplitude of sound


  Determines the loudness
• Frequency of sound


  Determines the pitch
• Speed of sound in air is 343 m/s, in water is 1493 m/s, and in steel is 5130 m/s
• Ultrasound


  Sound with a frequency greater than 20000 Hz
• Uses of ultrasound


  • Partially reflected back when it reaches a boundary between two media
  • Transceiver can emit ultrasound and record the reflected waves to find the distance of things below the surface
  • Used for SONAR and medical imaging without using ionising radiation

  
• Diffraction


  A type of wave behavior where waves bend around obstacles or through small openings
• Diffraction Process


  The bending of wavefronts around an obstacle or through a narrow opening due to wave properties, causing waves to spread out and change direction
• Types of Waves that Diffraction

  Light, sound, water, particle, mechanical, and seismic waves
• Diffraction and Frequency


  Diffraction affects the frequency of a wave, causing frequency shift and deviation, especially for high frequencies
• Diffraction and Wavelength


  Diffraction causes wavelength spread and reduction, especially in narrow openings and at high frequencies
• Frequency's Impact on Diffraction

  Higher frequencies cause more pronounced diffraction, lower frequencies cause less pronounced diffraction
• Frequency Dependence of Diffraction

  Frequency dependence of diffraction: high frequencies exhibit more pronounced diffraction; lower frequencies exhibit less pronounced diffraction
• Snell's Law


  Snell's Law relates the angle of incidence and refraction; refractive indices determine the bending of light