4.4 - Waves

• Wavelength

  Difference between two adjacent peaks
• Amplitude

  Maximum displacement from the equilibrium line
• Frequency

  Waves per second
• Time period

  Time taken for each particle to complete a full vibration
• Progressive wave

  A wave that carries energy from A to B
• Stationary waves

  A wave vibrating in a fixed length allowing energy to build up
• Longitudinal wave

  Particles vibrate parallel to the direction of travel

  Eg sound, ultrasound, primary seismic waves
• Transverse waves

  Particles vibrate perpendicular to the direction of travel

  Eg secondary seismic waves and EM waves
• Characteristics of Electromagnetic waves

  They can all travel without a medium

  Travel at speed of light in a vacuum

  Transverse waves

  Can all reflect, refract and defract
• 3 difference between stationary and progressive wave

  Progressive wave transfers energy All points have the same amplitude Neighbouring points are out of phase Stationary waves stores energy There are points with zero amplitude (nodes) and maximum amplitude (antinode) All points in a segment are in phase
• 2 types of progressive wave

  Transverse Longitudinal
• Coherent

  Waves that have a Constant phase difference
• Em waves order 


  Gamma. X-rays

  Ultra violet

  Visible light

  Infrared light

  Micro waves

  Radio waves
• Refractive index

  The ratio of speed of light in a vacuum to speed of light in a medium
• Snells law

  nsintheta=nsintheta
• Refractive index of glass

  1.5
• What decides the colour of a light wave 


  Frequency
• Which line are the angle of incidence and reflection measured from

  The normal line
• Which line are the angle of incidence and reflection measured from

  The normal line
• What is Diffraction

  Spreading out of a wave into a geometric shadow after passing through a gap
• Total internal reflection 


  When all the energy of the wave is internally reflected (when incident angle > critical angle)
• Critical angle


  The angle inside a medium beyond which waves are totally internally reflected
• Can a longitudinal wave be polarised

  No
• Inverse Square law

  Describes how energy is dissipated as it radiates from a point source
• Internal reflection

  When waves are reflected back into a dense medium
• Phase difference

  How much out of sync two waves are
• Superpose

  Occurs when waves meet and their displacements add together to produce a resultant wave form
• Fundamental frequency

  The natural frequency during to the longest wavelength that fits between fixed points
• Fundamental frequency

  The natural frequency during to the longest wavelength that fits between fixed points
• Node

  A point where the amplitude of the resultant wave is zero
• Antinode

  Where the amplitude of the resultant wave is a maximum
• Coherent waves

  Waves with a fixed phase difference between them
• Monochromatic

  Light waves at a single frequency
• Destructive interferences

  When waves superpose to produce a waveform with smaller displacement

  Antiphase
• Constructive interference

  Waves in phase produce a larger resultant intensity In phase
• Bright fringe

  Light waves meeting in phase to constructively interfere producing increased displacement
• Polarisation(PMT)

  The restriction of a wave so that it can only oscillate in a single plane. This can only occur in transverse waves
• Path difference (PMT)

  A measure in how far ahead a wave is compared to another wave
• Refraction (PMT)


  When a wave bends at a boundary between two materials due to a change in density causing it to speed up or slow down
• Best conditions for diffraction of a wave

  Gap size is approximately the same as the wavelength