Waves

• progressive wave: transfers energy and information from one place to another, but not matter
• standing/stationary wave: no net transfer of energy (comprised of nodes and anti-nodes)
• transverse: the oscillations are perpendicular to the direction of energy transfer
• wavelength: the distance between repeating points on consecutive waves
• amplitude: maximum displacement
• displacement: distance from zero displacement/equilibrium
• time period: time taken for one complete wave to pass a point
• frequency: the number of waves/oscillations per unit time (s)
• wavespeed = frequency x wavelength
• time period = 1/frequency
• • oscilloscopes can display wave traces
  • from this, we can calculate the time period of the wave and therefore the frequency
  • the time period is found by counting the number of divisions that one complete wave fills + multiply this by the value of division
• phase: a measure of position of a given point in a wave form/cycle
• phase difference: the difference between the displacement of two points on a wave/different waves
• in-phase: the waves have the same displacement at the same time
• anti-phase: the points are moving with opposite velocity
• phase difference = displacement/wavelength x 360
• EM Waves all:

  • travel at the speed of light in a vacuum
  • are transverse
  • can travel through a vacuum
  • can be reflected, refracted and diffracted
  • are comprised of two waves that are perpendicular to each other; an electric wave and a magnetic wave
• x-rays and gamma rays share wavelengths, the only difference between them is how they are created (gamma - nuclear decay, x-rays - electrons changing speed/direction
• law of reflection: angle of incidence = angle of reflection
• refraction:

  • as a wave travels between mediums, the wave changes speed and thus direction
• snells law:

  n1sin1=n2sin2

  n is the refractive index: the ratio of the speed of light through that material vs free space
• n= c/v
• sinc = n2/n1
• diffraction: the expanding of a wave due to passing through a gap or past an angle. maximum diffraction occurs when the wavelength and the size of the gap are of the same order of magnitude (with ref. to standard form)
• polarisation:

  • unpolarised light has oscillations in all possible planes
  • plane polarised light has oscillations in only one plane
  • polarising filters are used to only allow light to travel through in only one plane
• a single polarising filter will reduce the intensity of the light passing through it, due to absorbing the waves oscillating in planes that aren't the plane of transmission
• when two filters have the same plane of transmission, there is maximum intensity transmitted. as the second filter is rotated, the intensity of transmitted light varies, dropped to zero at 90 degrees.
• with three filters, when the central filter is rotated, the light transmitted varies from a zero to a maximum at 45 degrees.
• reflected light is partially plane polarised. this means that if reflected light is viewed through a polarising filter, the intensity will change depending on the angle of transmission
• intensity is the power per unit area
• when waves superpose, the resultant wave is the sum of the displacement of the individual waves
• when two progressive waves are in the same place at the same time, they can interfere (if they are of the same type)
• constructive interference: waves must be in phase
• destructive interference: the waves need to be in anti-phase
• interference is the superposition of two coherent waves
• coherent = constant phase difference, same wavelength, same frequency
• to form a standing wave:

  • two progressive waves (same type) must be travelling in opposite directions
  • they must have the same frequency/wavelength
  • they must have the same/similar amplitude
  • they superpose
• antinode: point of max amplitude
• node: point of zero amplitude
• the amplitude of each point on an s wave is different, from zero at the node, increasing to the antinode