Waves

• A progressive wave is which transfers energy from one point to another without transferring matter.
• Stationary waves are waves where there is no net energy transferred from one point to another
• Transverse waves are waves that oscillate perpendicular to the direction of energy transfer.
• Displacement is the distance a wave has travelled from its equilibrium position measured in meters (m)
• Amplitude is the maximum displacement from the equilibrium position, measured in meters (m)
• Wavelength is the minimum distance between two points oscillating in phase
• Electromagnetic waves are transverse waves
• Water waves are transverse waves
• S- waves are transverse waves
• Longitudinal waves have oscillations parallel to the direction of energy transfer.
• Compressions are the regions of longitudinal waves where the particles are closest together
• Rarefractions are the region of longitudinal waves where the particles are furthest apart
• The time taken for one complete wavelength to pass a given point is the period of the wave
• Frequency is the number of wavelengths passing a point per unit time, measured in hertz (Hz)


  f = $\frac{1}{T}$
• Wave speed is the distance travelled by a wave per unit time, measured in meters per second (m/s)


  v = f $\lambda$
• Intensity is defined as the radiant power passing through a surface per unit area.


  I = $\frac{P}{A}$
• Polarisation is where the oscillations of a transverse wave are limited to only one plane.
• Plane polarised waves are those that vibrate exclusively in one direction
• To polarise light, a filter is used to selectively absorb or transmit light of a particular orientation. Two filters at 90 degrees to each other will completely block the waves
• Investigating Light Polarisation:

  1. Position two polarising filters vertically and shine unpolarised light onto the first filter.
  2. This filter polarises the light vertically and the same occurs when light is shone onto the second also.
  3. Align both of the filters and gradually rotate the second filter
  4. The rotation will decrease the intensity of the light until a complete 90 degree rotation results in no light transmission.
• Investigating polarising microwaves:

  1. An emitter and detector are set up aligned with each other and a metal grille can be used as a polarising filter.
  2. The filter is then rotated and the amount of microwaves detected are recorded
  3. The maximum transmission of microwaves occurs when the grille is aligned with the waves and will decrease as it is moved past this orientation.
• Reflection is the change is direction of a wave when it hits a boundary, so that the wave remains in the original medium
• The law of reflection states that the angle of incidence is equal to the angle of reflection.
• Reflection can be observed with a ripple tank with water waves or a ray box for light waves
• Refraction is the change in direction of a wave as it changes speed when it passes from one medium to another
• When a wave enters a more dense medium, it slows down and refracts towards the normal line
• When a wave enters a less dense medium, it speeds up and refracts away from the normal.
• Total internal reflection occurs when light moves from a denser medium to one with a lower refractive index.
• At the critical angle, the angle of refraction is 90$\degree$ and travels along the the barrier between mediums
• If the angle of incidence is greater than the critical angle, all of the light is reflected back into the original medium.
• Superposition of waves is where two waves overlap at a point in space.
• The principle of superposition of waves states that when two waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves.
• Constructive interference is the superposition of two waves in phase so that the resultant wave has a greater amplitude than the original waves
• Destructive interference is the superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has a smaller amplitude that the original waves
• Phase difference is the difference between displacements of particles along a wave or the difference between the displacements of particles on different waves
• When waves are in phase the particles are oscillating perfectly in time with each other
• When waves are in antiphase, the particles are oscillating completely out of step with each other.
• Path difference is the difference in the distance travelled by two waves from the source to a specific point
• Constructive interference occurs when the path difference is an integer number of wavelengths


  path difference = n $\lambda$
• Destructive interference occurs when there is a path difference equal to an odd number of half wavelengths 


  path difference = $(n+\frac{1}{2})\lambda$