Section C: Waves

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Properties of Waves

ALL waves transfer energy

Transverse waves - oscillations perpendicular to direction of movement of the wave (e.g all Electromagnetic Waves)

Longitudinal waves - oscillations parallel to the direction of the movement of the wave (e.g Sound Waves)

Amplitude is the maximum displacement from the equilibrium to the peak/trough

Time period is the time taken for a source to produce a wave

Wavelength is the distance between a particular point on a wave and the same point on the next wave (e.g peak to peak)

Frequency (Hz) is the number of waves produced each second by a source / number of waves passing a particular point each second

All waves reflect, refract and diffract

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Properties of Waves - Reflection, Refraction & Dif

Reflection:

  • The angle of incidence (i) = The angle of refraction (r
  • When waves strike a concave barrier, they converge
  • When waves strike a convex barrier, they diverge (spread out)

Refraction:

When waves travel from a less dense material (water) into a more optically dense material (glass) the wave slows down and bends towards the normal

Diffraction:

  • If the gap of the barrier is much wider than the wavelength of the waves, most of the waves continue in a straigh line
  • If the gap of the barrier is about the same width of the wavelength of the wave, most waves will spread out and diffract
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Electromagnetic Spectrum

They (are) ALL:

  • transfer energy
  • transverse waves
  • travel at the speed of light (3 x 10^8 m/s)
  • reflect, refract and diffract

Radio waves (TV transmitters), Micro waves (Mobile comms.), Infra Red (Remote controls), Visible Light (seeing, optical fibres), Ultra Violet (Tanning lamps), X Rays (X-radiography - bones), Gamma Rays (radiotheraphy, sterilisation)

Red has a longer wavelength than violet

The shorter the wavelength, the more energetic the wave

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Light Waves

Properties of an image created in a plane mirror:

  • The image is as far behind the mirror as the object is in front
  • The image is the same size as the object
  • The image is virtual - cannot be produced on a screen
  • The image is laterally inverted
  • The image is the same colour

Total internal reflection

As the angle increases, so does too the angle of refraction until the angle of refraction is 90 degrees - this is called the critical angle. If the angle of incidence is increased even more so the angle of refraction is more than 90 degrees, the light is reflected. (ONLY HAPPENS FROM MORE DENSE TO LESS DENSE)

Uses of TIR:

  • Bicycle reflectors
  • Optical Fibres
  • Prismatic Periscope
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Sound Waves

  • Speakers push air molecules closer together (this is called a compression
  • Behind these compressions, the molecules are spread out (this is called a rarefaction)
  • Sound waves are LONGITUDINAL
  • Can be measured using echoes
  • Reflected sound waves can be used to tell ships about the depth of the sea beneath them
  • Sound waves can be diffracted - that's why we can hear people from behind an open door

Pitch & Frequency

   Small objects (e.g strings on a violin) vibrate quickly and produce sound with a high frequency.

Frequency = Pitch

   Large objects (e.g strings on a cello) vibrate slower and produce sound waves with a lower frequency

Human Audible Range : 20 Hz - 20 000 Hz

Amplitude = Volume

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