PMT: waves

    Cards (81)

    • Progressive wave
      Transfers energy without transferring material, made up of particles of a medium (or field) oscillating
    • Wave properties
      • Amplitude
      • Frequency, f
      • Wavelength, λ
      • Speed, c
      • Phase
      • Phase difference
      • Period, T
    • Amplitude
      A wave's maximum displacement from the equilibrium position (units are m)
    • Frequency, f
      The number of complete oscillations passing through a point per second (units are Hz)
    • Wavelength, λ
      The length of one whole oscillation (e.g. the distance between successive peaks/troughs) (units are m)
    • Speed, c
      Distance travelled by the wave per unit time (units are m/s)
    • Phase
      The position of a certain point on a wave cycle (units are radians, degrees or fractions of a cycle)
    • Phase difference
      How much a particle/wave lags behind another particle/wave (units are radians, degrees or fractions of a cycle)
    • Period, T
      Time taken for one full oscillation (units are s)
    • Two points on a wave are in phase if they are both at the same point of the wave cycle, they will have the same displacement and velocity and their phase difference will be a multiple of 360° (2π radians), they do not need the same amplitude, only the same frequency and wavelength
    • Two points are completely out of phase when they're an odd integer of half cycles apart e.g. 5 half cycles apart where one half cycle is 180° (π radians)
    • Wave speed, c
      c =
    • Wave frequency, f
      f = 1/T
    • Transverse waves
      Oscillation of particles (or fields) is at right angles to the direction of energy transfer
    • Transverse waves
      • All electromagnetic (EM) waves
      • Waves seen on a string, when it's attached to a signal generator
    • Longitudinal waves
      Oscillation of particles is parallel to the direction of energy transfer, made up of compressions and rarefactions, can't travel in a vacuum
    • Longitudinal waves
      • Sound
    • Polarised wave
      Oscillates in only one plane (e.g only up and down), 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
    • Antinodes
      Regions of maximum amplitude where the waves meet in phase, constructive interference occurs
    • Nodes
      Regions of no displacement where the waves meet completely out of phase, destructive interference occurs
    • First harmonic frequency
      f = (1/2L) * sqrt(T/μ)
    • You can double the first harmonic frequency to find the second harmonic where there are 2 antinodes, you triple the first harmonic frequency to get the third harmonic where there are 3 antinodes, and so on for the nth harmonic
    • Examples of stationary waves
      • Stationary microwaves
      • Stationary sound waves
    • Path difference
      The difference in the distance travelled by two waves
    • Coherent light source
      Has the same frequency and wavelength and a fixed phase difference
    • Examples of coherent light sources
      • Lasers
    • Young's double slit experiment
      Demonstrates interference of light from two-sources
    • Fringe spacing, w
      w = (λD)/s
    • Using white light instead of monochromatic laser light gives wider maxima and a less intense diffraction pattern with a central white fringe with alternating bright fringes which are spectra, violet is closest to the central maximum and red furthest
    • Lasers can permanently damage your eyesight therefore, when using lasers there are several safety precautions, which must be followed</b>
    • Safety precautions when using lasers
      • Wear laser safety goggles
      • Don't shine the laser at reflective surfaces
      • Display a warning sign
      • Never shine the laser at a person
    • The type of interference described above can also be demonstrated in sound waves through a very similar process, however instead of using a double slit, you could use two speakers connected to the same signal generator. And the intensity of the wave can be measured using a microphone to find the maxima (equivalent to light fringes), and minima (equivalent to dark fringes)
    • Evidence for the wave nature of light was provided by Young's double slit experiment because diffraction and interference are wave properties, and so proved that EM radiation must act as a wave (at least some of the time)
    • Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community
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