Waves 1

• A progressive wave is an oscillation that travels through matter or sometimes a vacuum, transferring energy
• Sound is a progressive wave as vibrations travel to the ears not air particles - they vibrate in a plane parallel to the direction of energy transfer
• A transverse wave has oscillations perpendicular to the direction of energy transfer
• oscillation - a backwards and forwards motion about an equilibrium point
• Time period is the time taken for one full oscillation or the time taken for the wave to move one whole wavelength past a point
• Time period is inversely proportional to frequency and k is 1
• wavespeed = frequency x wavelength
• A wave profile is a graph showing the displacement of the particles in the wave against the distance along the wave
• Phase difference is the difference between the displacement of particles along a wave or the difference between the displacements of particles on different waves
• If 2 particles are in phase, their oscillations are perfectly in step with each other and have a phase difference of 0

  They both reach their maximum positive and maximum negative points at the same time
• phase difference $\phi$ = distance (x/m) / wavelength ($\lambda$/m)
• Reflection is when a wave changes direction at a boundary between 2 different media, remaining in the original medium
• Law of reflection - angle of incidence is equal to the angle of reflection
• Refraction occurs when a wave changes direction as it changes speed when it travels from one medium to another

  when a wave refracts there is always some reflection off the surface (partial reflection)
• If a wave slows down when entering a medium, it refracts towards the normal and wavelength decreases
• If a wave speeds upon entering a different medium it refracts away from the normal
• Generally sound waves speed up when entering a denser medium
• Light waves generally slow down when entering a denser medium
• When water waves enter shallower water, it slows down and the wavelength gets shorter
• Diffraction occurs when waves pass through a gap or travel around an object

  Speed, frequency, and wavelength don't change when a wave is diffracted
• Diffraction is greatest when the size of the gap or object is the same as the wavelength
• Polarisation means that particles oscillate along one direction only meaning the plane is confined to a single plane
• If a wave is plane polarised, the plane of oscillation contains the oscillation of the particles and the direction of travel of the wave
• Longitudinal waves cannot be plane polarised as oscillations are always parallel to the direction of energy transfer and are already limited to one direction of energy transfer
• Reflected light becomes partially polarised - there are more waves oscillating in one plane but the light is not completely plane polarised

  Most light waves can be polarised through polarising filters which only allow light oscillating in one direction
• Intensity - the radiant power passing through a surface per unit area
• intensity (Wm^-2) = radiant power (W)/Cross sectional area (m^2)
• Intensity of a wave reduces as it spreads out from a point source as the cross sectional area increases
• Intensity is directly proportional to amplitude^2 and inversely proportional to distance^2
• Electromagnetic waves can travel through a vacuum. They can be thought of as electric and magnetic fields oscillating perpendicular to each other
• Radio waves

  Wavelength : 1000000 - 0.1 m

  Frequency : 3 x 10^9 - 300 Hz
• Microwaves

  Wavelength : 0.1 - 10^-3 m

  Frequency : 300 - 3 x 10^11 Hz
• Infrared

  Wavelength : 7 x 10^-7 - 10^-3 m

  Frequency : 3x 10^11 - 4 x 10^14 Hz
• Visible light

  Wavelength : 4 x 10^-7 - 7 x 10^-7 m

  Frequency : 4 x 10^14 - 7.5 x 10^14 Hz
• Ultraviolet

  Wavelength : 10^-8 - 4 x 10^-7 m

  Frequency : 7.5 x 10^14 - 3 x 10^16 Hz
• X-rays

  Wavelength : 10^-13 - 10^-8 m

  Frequency : 3 x 10^16 - 3 x 10^21 Hz
• Gamma rays

  Wavelength : 10^-16 - 10^-10 m

  Frequency : 3 x 10^24 - 3 x 10^18 Hz
• X rays and gamma rays have a cross over meaning the origin of the wave determines its classification

  Gamma rays come from unstable atomic nuclei

  X rays come from fast moving particles
• Properties of EM waves:

  Can be reflected, refracted, diffracted and plane polarised
• Unpolarised light is light with a random, time varying polarisation - it vibrates in more than one plane