TOPIC 3 (physics)

• Progressive wave


  Transfers energy without transferring material, made up of particles of a medium (or field) oscillating
• Properties of a wave

  • Amplitude
  • Frequency
  • Wavelength
  • Speed
  • Phase
  • Phase difference
  • Period

  
• In phase


  Two points on a wave are at the same point of the wave cycle, have the same displacement and velocity, and their phase difference is a multiple of 360° (2π radians)
• Completely out of phase


  Two points are an odd integer of half cycles apart
• Wave speed


  c = fλ

  
• Wave frequency


  f = 1/T

  
• Transverse wave


  Oscillation of particles (or fields) is at right angles to the direction of energy transfer
• Longitudinal wave


  Oscillation of particles is parallel to the direction of energy transfer, made up of compressions and rarefactions
• Polarised wave


  Oscillates in only one plane, only transverse waves can be polarised
• Applications of polarisation


  • Polaroid sunglasses
  • TV and radio signals
• Superposition


  Displacements of two waves are combined as they pass each other, the resultant displacement is the vector sum of each wave's displacement
• Constructive interference


  Occurs when 2 waves have displacement in the same direction
• Destructive interference


  Occurs when one wave has positive displacement and the other has negative displacement, if the waves have equal but opposite displacements, total destructive interference occurs
• Stationary wave


  Formed from the superposition of 2 progressive waves travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude
• No energy is transferred by a stationary wave
• Antinode


  Region of maximum amplitude where waves meet in phase
• Node


  Region of no displacement where waves meet completely out of phase
• Formation of a stationary wave on a string

  Wave travelling down the string from the oscillator is reflected at the fixed end and travels back, causing superposition and forming a stationary wave
• Frequency of first harmonic stationary wave

  f = (1/2L)√(T/μ)

  
• Frequency of higher harmonics is an integer multiple of the first harmonic frequency

  
• Examples of stationary waves


  • Stationary microwaves
  • Stationary sound waves
• Path difference


  Difference in the distance travelled by two waves
• Coherent light source


  Has the same frequency and wavelength and a fixed phase difference

  
• Young's double slit experiment

  Shine a coherent light source through 2 slits, each slit acts as a coherent point source making a pattern of light and dark fringes
• Fringe spacing in Young's double slit experiment


  w = (λD)/s
• White light interference


  Gives wider maxima and a less intense diffraction pattern with a central white fringe and alternating bright fringes which are spectra

  
• Lasers can permanently damage eyesight, so safety precautions must be followed
• Young's double slit experiment provided evidence for the wave nature of light
• Diffraction


  Spreading out of waves when they pass through or around a gap
• Greatest diffraction occurs when the gap is the same size as the wavelength
• Diffraction around an obstacle is less noticeable when the obstacle is wider compared to the wavelength
• Diffraction pattern from a single slit

  Has a bright central fringe double the width of all other fringes, with alternating dark and bright fringes on either side
• Understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community
• Diffraction


  The spreading out of waves when they pass through or around a gap
• Diffraction


  • The greatest diffraction occurs when the gap is the same size as the wavelength
  • When the gap is smaller than the wavelength most waves are reflected
  • When the gap is larger there is less noticeable diffraction
  • When a wave meets an obstacle you get diffraction round the edges
  • The wider the obstacle compared to the wavelength, the less diffraction
• Diffraction of monochromatic light through a single slit

  1. Light forms an interference pattern of light and dark fringes

  2. Bright central fringe is double the width of all other fringes

  3. Bright fringes are caused by constructive interference

  4. Dark fringes are caused by destructive interference

  5. Intensity of fringes decreases from central fringe

  
• White light diffraction


  • White light is made up of all colours/wavelengths
  • Different wavelengths are diffracted by different amounts
  • Diffraction pattern has a central white maximum with alternating bright fringes which are spectra
  • Violet is closest to central maximum, red is furthest away

  
• Increasing slit width


  Decreases amount of diffraction, central maximum becomes narrower and intensity increases
• Increasing wavelength


  Increases amount of diffraction, central maximum becomes wider and intensity decreases

  
• Diffraction grating


  • Slide containing many equally spaced slits very close together
  • Interference pattern is much sharper and brighter than double slit
  • Measurements of slit widths are more accurate