P3- waves

Wave is a vibration through a substance.

λ=Wavelength – length of one whole wave cycle

A=Amplitude – max magnitude of displacement from equilibrium.

F=Frequency – number of cycles per second passing through a point

T=Time period – the time per one complete wave to pass a fixed point.



Phase difference- the amount one wave lags behind another measured as a fraction of a cycle.(2pid/λ)

Longitude and transverse waves:

Longitude waves – are waves in which the direction of vibration of the particles as parallel to the direction in which the wave travels.

Example: sound waves

Transverse waves – are waves in which the direction of vibration is perpendicular to the direction in which the waves travel.

Example: electromagnetic waves

Polansation – transverse waves can be plain polanised so the vibrations stay in one place only.

Polarized glasses reduce the glare of light reflected by water or glass. The reflected light is plane polanised and the intensity is reduced when it passes through the polaroid glasses.


Stationary waves:

The principle of super position states that when two waves meet the total displacement at a point is equal to the sum of the individual displacements at that point.

Formation of a stationary wave:

A stationary wave can be formed on a string with a fixed end. If a progressive wave is sent down the string it hits the fixed end and reflects back. As the two progressive waves pass through each other super position occurs when they are in phase they reinforce each other and when in antiphase they cancel each other. This creates a wave that appears to be stationary.




Stationary wave  the super position of two progressive waves with the same frequency wavelength moving in opposite direction.

Node – point of no displacement

Antinode – point of maximum displacement.


Diffraction:  the spreading of waves where they pass through a gap or round an obstacle

When the size of the slit is equal to the wavelength, the largest diffraction will occur. As the wavelength of the light is very small when diffracting light a smaller slit is better.

Youngs double slit

  • the slit deffracts the light to create a coherent source of waves.

Coherent light: has a constant phase difference.

  • This means the light is coherent when it reaches the double slits
  • Each slit diffracts the light and the two slits of diffracted light interfere with each other creating a constant interference pattern
  • where two waves reinforce each other a bright fringe is formed. where destructive fringes occurs a clark fring shows.
  • using a coherent light source like a laser means you dont need the single slit at the start

  • where the waves reinforce each other they curve in a phase and create a bright fringe
  • dark fringe are formed when waves are 180out of phase

  • therefore in an experiment you want d to be as large as possible to make it easier and more accurate to measure.  this reduces the percentage uncertainty

wavelength and color


increase the wavelength increased fringe spacing

Red light                                               blue wavelength

high wavelength                                   low wavelength

low frequency                                       high frequency





white light

when white light is diffracted each of its components with different wavelength (including the red and blue above) diffract slightly differently. this means the light to split mto its composing colors

diffraction grating

the pattern seen with lots of slits (diffraction grating) is  similar to double slit (bright and dark fringes) but there are fewer fringes and the gaps between them are much larger

double slit different grating


Refraction: change in direction of wave when it crosses a boundary where its speed changes

refraction of air =1

Snells law:

total internal reflection(TIR) can only take place y:

  • the incident substances has a larger refraction index than the other substance
  • the angle of incidence exceeds the critical angle

optical fibers



  • improves tensile strength of cable
  • increased critical angle needed for TIR.
  • stops core being scratched
  • stops light traveling from one fiber to another


  • core must be narrow to prevent model dispersion. light needs to take short route otherwise it will merge with the next pulse