Waves

Cards (31)

  • Waves
    Transfer energy and information without transferring matter; the particles oscillate about a fixed point
  • Transverse waves
    • Have peaks and troughs
    • Vibrations are at right angles to the direction of travel
    • An example is light
  • Longitudinal waves
    • Consists of compressions (particles pushed together) and rarefactions (particles moved apart)
    • Vibrations are in the same direction as the direction of travel
    • An example is sound
  • Amplitude
    The distance from the equilibrium position to the maximum displacement
  • Wavefront
    A line joining points on a wave at the same point in their wave cycle at a given time
  • Frequency
    The number of waves that pass a single point per second
  • Wavelength
    The distance between a point on one wave and the same point on the next wave
  • Time period
    The time taken for one complete wave to pass a fixed point
  • Wave speed
    Speed = Frequency x Wavelength
  • Frequency
    The reciprocal of the time period, measured in Hertz (Hz)
  • Doppler effect
    If a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength
  • Reflection
    1. Waves can be reflected when they travel from a medium of low optical density to one of much higher optical density
    2. Angle of incidence = angle of reflection
    3. Frequency, wavelength, and speed are all unchanged
  • Refraction
    1. Waves can be refracted, which is when the speed of a wave changes when it enters a new medium
    2. If the wave enters a denser medium, its speed decreases and it bends towards the normal
    3. If the wave enters a less dense medium, its speed increases and it bends away from the normal
    4. Frequency stays the same but the wavelength changes
  • Electromagnetic spectrum
    • Radio waves
    • Microwaves
    • Infrared radiation
    • Visible light
    • Ultraviolet light
    • X-rays
    • Gamma radiation
  • All electromagnetic waves travel with the same high speed in a vacuum and approximately the same speed in air
  • Uses of electromagnetic waves
    • Radio waves for radio and television communications
    • Microwaves for satellite transmissions and cooking
    • Infrared radiation for heaters and night vision equipment
    • Visible light for fibre optics and photography
    • Ultraviolet light for fluorescent lamps
    • X-rays for medical imaging and security
    • Gamma radiation for sterilising food and medical equipment
  • Hazards of electromagnetic waves
    • Microwaves can cause internal heating of body tissues
    • Infrared radiation can cause skin burns
    • Ultraviolet light exposure increases the risk of skin cancer and blindness
    • X-rays and Gamma rays are ionising radiation that can cause mutations leading to cancer
  • Light waves
    Transverse waves that can be reflected and refracted
  • Reflection of light
    Light reflects at a plane mirror and forms an image
  • Refraction of light
    1. When light enters a more optically dense medium, the angle of incidence is greater than the angle of refraction
    2. The opposite is true when light enters a less optically dense medium
  • Snell's law
    Relates the angle of incidence and the angle of refraction to the refractive index of a medium
  • Total internal reflection
    1. At a certain angle of incidence called the critical angle, the light will travel along the boundary between the two media
    2. Total internal reflection occurs when the angle of incidence is greater than the critical angle and the light reflects back into the medium
    3. For total internal reflection to occur, the light must be travelling from a more optically dense medium into a less optically dense medium
  • Optical fibre
    A long thin rod of glass surrounded by cladding which uses total internal reflection to transfer information by light, even when bent
  • Uses of optical fibres
    • Medicine (endoscopes, inside-body flexible cameras)
    • Communications (high speed data transfer)
  • Sound waves

    Longitudinal waves that can be reflected and refracted
  • Audible frequency range
    20 Hz to 20000 Hz for a healthy human ear
  • Measuring speed of sound in air
    Make a noise at a known, large distance from a solid wall and record the time for the echo (reflected sound) to be heard, then use speed = distance/time
  • Oscilloscope
    Can be used to display a sound wave and find its frequency and amplitude
  • Amplitude of sound wave
    The greater the amplitude, the louder the sound
  • Frequency of sound wave
    The greater the frequency, the higher the pitch
  • Sound wave characteristics
    • Quiet and low pitched
    • Loud and low pitched
    • Loud and high pitched