waves

• amplitude is the maximum displacement of a vibrating particle from its equilibrium position
• the wavelength is the shortest distance between two equal points on a wave
• frequency is the number of waves passing a point per second, measured in hertz (Hz)
• wavespeed is the distance travelled by a wave each second
• a progressive wave is a wave whose oscillations travel and transfer energy
• longitudinal waves are waves whose oscillations are parallel to the direction of energy travel
• transverse waves are waves whose oscillations are perpendicular to the direction of energy travel
• only transverse waves can be polarised
• polarisation of waves: meaning all the waves are oscillating in the same plane.
• polarisation can be used in things such as polaroid sunglasses to reduce glare or in a camera to enhance the image.
• transverse waves have peaks and troughs where the oscillating particles are at maximum displacement from their equilibrium position.
• when a longitudinal wave passes through a medium, it creates a series of compressions and rarefractions
• reflection occurs when a wave changes direction at a boundary between two different media, remaining in the original medium.
• the law of reflection states that the angle of incidence is equal to the angle of reflection
• refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another
• when a wave refracts there is always partial reflection
• when EM waves enter a denser medium, the waves slow down and the wavelengths are stretched
• when sound waves enter a denser medium, they speed up and compress
• a wave will refract towards the normal if it slows down during refraction
• when drawing ray diagrams, always measure angles to the normal
• Polarisation:

  • Only transverse waves (EM)
  • Occurs when the oscillation of a wave is restricted to one place
  • Results in plane polarised waves
  • Longitudinal waves cannot polarise because the direction of energy transfer is already in one plane
• To demonstrate polarisation of visible light, polarising filters can be used by placing two filters on top of each other and rotating one filter by 90°
• As light passes through the filter which is polarised in one direction, the light polarised in the perpendicular direction cannot pass through, leading to a decrease in light intensity
• Intensity:

  • Defined as the radiant power passing at right angles through a surface per unit area
  • Formula: I = P/A
  • Units: watts per metre squared (Wm^-2)
  • The intensity of light is inversely proportional to the square of the radius, and can also be related to the amplitude of the wave (intensity ∞ Amplitude squared)
• Refraction:

  • Occurs because when a ray enters a new medium, its speed changes
  • Refractive index (n) is used to determine the angle of refraction into the medium (n =)
• Total internal reflection:

  • Occurs at a boundary between two transparent media, with no refraction
  • All of the light incident on the boundary is reflected back into the original medium
• Principle of superposition:

  • When two waves meet at a point, the resultant displacement of the wave at that point is equal to the sum of the displacements of the individual waves
• Coherent waves:

  • Waves emitted with a constant and unchanging phase difference
• Increasing the temperature increases the speed of sound due to increased particle vibrations.
• Progressive wave


  An oscillation that travels through matter (or in some cases a vacuum), transferring energy from one place to another, but not transferring any matter
• Progressive waves


  • The particles in the matter vibrate as the wave passes through them, but they do not move along with the wave
  • There are two types: transverse and longitudinal
• Transverse wave


  The oscillations are perpendicular to the direction of wave travel, such as electromagnetic waves and waves on the surface of water
• Longitudinal wave


  The oscillations are parallel to the direction of energy transfer, such as sound waves
• Displacement


  The distance from the equilibrium position in a particular direction
• Amplitude


  The maximum displacement from the origin
• Wavelength


  The minimum distance between two adjacent points on a wave oscillating in phase
• Period


  The time taken for a full oscillation of one wavelength to pass a given point
• Frequency


  The number of complete oscillations passing a given point per unit time
• Wave speed


  The distance travelled by a wave per unit time
• Phase difference


  The difference in displacement of particles along a wave, or in 2 different waves, measured in radians