Waves

• A progressive wave carries energy from one place to another without transferring any material
• Displacement - How far a point has moved from its undisturbed position
• Amplitude - Maximum magnitude of displacement from equilibrium position.
• Wavelength - The length of one whole wave oscillation
• Period - Time taken for one whole wave cycle
• Frequency - Number of whole waves per second
• Phase - A measurement of the position of a certain point along the wave
• Phase difference - The amount by while one wave lags behind another wave OR The difference in phase between two waves
• In a transverse wave the oscillation of particles occurs at right angles to the direction of the wave. An example of a transverse wave is any electromagnetic wave such as microwaves
• Waves can be either Transverse or Longitudinal waves
• In longitudinal waves the oscillations of particles occur in the direction of energy travel
• Frequency = 1/Time period
• Wave speed (v) = distance traveled (d) / Time taken (s)
• Wave speed (v) = frequency (f) x wavelength (λ)
• Intensity (I) = Power (P) / Area (A)
• Intensity is directly proportional to amplitude squared
• Electromagnetic waves:

  • Travel at the speed of light in a vacuum
  • They can be refracted, diffracted, reflected and can undergo interference
  • They can be polarised
• Types of EM waves (In order and with wavelength):

  • Radio waves, 10^-1 - 10^6
  • Microwaves, 10^-3 - 10^-1
  • Infrared, 7x10^-7 - 10^-3
  • Visible light, 4x10^-7 - 7x10^-7
  • Ultraviolet, 10^-8 - 4x10^-7
  • X-rays, 10^-13 - 10^-8
  • Gamma rays, 10^-16 - 10^-10
• A polarising filter is used to polarise light (And other waves)
• Polarising filters only transmits vibrations in one direction. If you have two polarising filters at 90 degree angles to each other then no light will get through.
• Polarising filters don't work on microwaves due to their longer wavelength. Instead a metal grill are used to polarise microwaves
• Reflection is when a wave is bounced back when it hits a boundary
• angle of incidence = angle of reflection
• Refraction is the way a wave changes direction as it passes from one medium to another. If the ray passes towards the normal then the wave is slowing down. If the wave passes away from the normal then it is getting faster.
• You can use a ripple tank to show the wave effects of reflection and refraction.
• To show reflection in a ripple tank, set up a signal generator connected to a paddle to move the water. Place a barrier in the tank at an angle to the wave front. You should be able to see the wave reflecting off the barrier
• To show refraction in a ripple tank, place two tanks side by side with different depths of water. Connect them together so that they have the same frequency but different amplitudes. The waves will travel through both tanks and meet again at the end. They will not line up because the speed of sound is slower in deeper water. This causes the wavefronts to bend or refract
• When light travels from air into glass, the light slows down which means the angle of incidence is greater than the angle of refraction
• The equation for refraction is sin(i) / v1 = sin(r) / v2 where i is the incident angle, r is the reflected angle, v1 is the velocity of the first medium and v2 is the velocity of the second medium
• refractive index (n) = speed of light in vacuum(c) / speed of light in material (v)
• Snell's law:

  • If light is passing through a boundary between two materials you can uses Snell's law to calculate unknown angles or refractive indices
• nSin(feta) = constant
• n_1 * sin(feta_1) = n_2 * sin(feta_2)
• To find refractive index:

  • Place a glass rectangular box on paper and draw round it
  • Use a ray box to shine light through the glass
  • Trace the path of the incoming and outcoming light rays
  • Remove the block and join the two lines, this shows the path the light took in the glass
  • Measure the angle of incidence and the angle of refraction where the light enters and leaves the box
• sin(C) = n_1 / n_2 when n_1 > n_2
• sin(C) = 1/n
• When the angle of incidence is greater than the critical angle, the light is reflected back inside the material. This is called total internal reflection
• Superposition happens when two or more waves pass through each other
• In supper position the displacement of each wave combines
• When two waves meet, if their displacement are in the same direction then the displacement combines to form an even bigger displacement. This is called constructive superposition