Waves

Waves

1. Wave Basics

   • Waves transfer energy from one place to the other without transferring any matter (stuff)
   • Waves have Amplitude, Wavelength and Frequency
     • 1. The amplitude is the displacement from the rest position to the crest (not from a trough to the crest)
       • trough - lowest point in a wave
       • crest - highest point in a wave
     • 2. The wavelength is the length of a full cycle of the wave e.g. from crest to crest
     • 3. Frequency is the number of complete waves passing a certian point per second OR the number of waves produced by a source each second. Frequency is measured in hertz (Hz). 1 Hz is 1 wave per second
   • Transverse waves have sideways vibrations
     • 1. Light and all other EM waves
     • 2. Ripples on water
     • 3. Waves on strings
     • 4. A slinky spring wiggled up and down
     • In TRANSVERSE waves the vibrations are PERPENDICULAR (at 90°) to the DIRECTION OF ENERGY TRANSFER of the wave
   • Longitudinal waves have vibrations along the same line
     • Examples of Longitudinal Waves
       • 1. Sound waves and ultrasound
       • 2. Shock waves e.g. seismic waves
       • 3. A slinky spring when you push the end (Sown in picture example)
     • In LONGITUDINAL waves the vibrations are PARALLEL to the DIRECTION OF ENERGY TRANSFER of the wave

2. Wave Speed = Frequency x Wavelength

   • The following equation applies to all waves.
     • v = f x λ
       • V = speed m/s (v is for velocity)
       • F = Frequency Hz
       • λ = Wavelength m (Its the Greek letter for 'Lambda)
       • It could also be written as the following:
         • Speed (m/s) = Frequency (Hz) x Wavelength (m)
         • Example
           • A radio station has a frequency of 92.2 x 1,000,000 Hz. Find its wavelength (The speed of all EM waves is 3 x 108 (10 to the power 8) m/s.)
             • Answer: You are trying to find λ using f and v, so you've got to rearrange the equation.
               • So λ = v ÷ f = 3 x 10 (to the power 8) ÷ 9.22 x 10 (to the power 7) = 3.25m
                 • The speed of a wave is usually independent of the frequency or amplitude of the wave

3. Waves Properties

   • All waves can be reflected, refracted and diffracted
     • 1. When waves arrive at an obstacle (or meet a new material), their direction of travel can be changed
     • 2. This can only happen by reflection or by refraction or doffraction
   • Reflection of light lets us see things
     • 1. Reflection of light is what allows us to see objects. Light bounces off them into out eyes.
     • 2. When light travelling in the same direction reflects from an uneven surface such as a piece of paper, the light reflects off in different angles
     • 3. When light travelling in the same direction reflects from an even surface (such as something smooth and shiny such as a mirror) then its all reflected at the same angle and you get a clear reflection

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