6-Waves

• waves

  • waves transfer energy from one place to another without transferring matter
  • waves vibrate/oscillate to travel
• displacement-distance graphs

  • distance is how far the wave travelled from the starting point
  • displacement is how far the wave oscillated from the equilibrium point
  • amplitude is the maximum displacement
  • wavelength is the distance of one entire oscillation

  A) wavelength

  B) amplitude

  
• displacement-time graphs

  • time period is the time it takes to complete one complete oscillation
  • it can be used to work out frequency

  A) time period

  
• frequency

  • frequency = 1 divided by time period
  • F = 1 / T
  • units:
  • frequency - hertz (Hz)
  • time period - second (s)
  • frequency is the number of complete oscillations per second
• wave speed

  • wave speed = frequency x wavelength
  • V = f x λ
  • units:
  • wave speed - m/s
  • frequency - hertz (Hz)
  • wavelength - metres (m)
• transverse waves

  • transverse waves have oscillations that are perpendicular to the direction of energy transfer
  • most waves are transverse such as electromagnetic (light, radio), ripples/waves in water, waves of strings

  
• longitudinal waves

  • longitudinal waves have oscillations that are parallel to the direction of energy transfer
  • this causes some regions to be more spread out and some to be more compressed because the waves are vibrating back and forth
  • longitudinal waves include sound, seismic p waves (shock waves)

  
• reflection of waves

  • waves are sometimes reflected
  • the things that can happen to a wave - absorbed, transmitted, reflected
  • what happens depends on the wavelength and the properties of the two materials
• ray diagrams

  • the angle of incidence is always equal to the angle of reflection

  A) incoming ray

  B) point of incidence

  C) angle of incidence

  D) reflected ray

  E) normal

  F) angle of reflection

  G) boundary

  
• types of reflection

  • specular reflection - flat/smooth surface - normals are all in the same direction so all incoming light rays will be reflected in the same direction - clear image
  • diffuse reflection - rough/bumpy surface - light rays coming in the same direction but surface has different normals so the light is reflected in all different directions - no image
• refraction

  • refraction is the change in direction of a wave as it passes from one medium to another
  • refraction causes a wave to change it's speed due to the density of the material
• ray diagrams for refraction

  • the refracted line should be halfway between the angle of refraction
  • frequency always stays the same, only the wavelength changes
  • different wavelengths of lights are refracted by different amounts - white light reflected through triangular prism then would shine rainbow

  A) incidence ray

  B) angle of incidence

  C) point of incidence

  D) angle of refraction

  E) refracted ray

  F) normal

  G) emergent ray

  
• electromagnetic waves

  • they are all transverse
  • in a vacuum they travel at the same speed of 3 x 10 to the power of 8 m/s
  • they can be reflected, absorbed, transmitted
  • they differ in wavelength and frequency - wavelengths get shorter and frequency gets higher
  • our eyes are only able to detect visible light

  
• order of electromagnetic waves

  1. radio
  2. micro
  3. infrared
  4. visible light
  5. ultraviolet
  6. x-ray
  7. gamma
• radio waves

  • they can be generated using alternating current (electricity) because they are made of oscillating charges
  • oscilloscope - displays frequency of alternating current
  • transmitter - generates wave
  • receiver - absorbs energy generates alternating current
  • used in communication

  A) transmitter

  B) receiver

  C) oscilloscope

  
• radio waves - communication

  • long, short, very short waves
  • long - can be transmitted huge distances as they diffract (bend) around the earth
  • short - can be transmitted long distances but can't diffract instead they're reflected from the ionosphere (electrically charged layer in atmosphere), short range distances like Bluetooth
  • very short - TV and FM radio they travel directly from the transmitter to the receiver
• micro waves

  • relatively long wavelengths and low frequencies
  • those not absorbed by water molecules - used for satellite communication, they are received by satellite and reflected onto satellite dish
  • those absorbed by water molecules - used in microwave ovens to heat food as waves are absorbed by water molecules and energy spreads throughout it via conduction and convection
  • only dangerous in high quantities
• infrared

  • relatively long wavelengths and low frequencies
  • emitted from all objects that have thermal energy
  • used by infrared cameras to see in the dark and spot living organisms
  • used in cooking - ovens and grills that emit lots of infrared radiation so transfer heat energy - doesn't penetrate the surface
  • used in electric heaters - electrical energy heats metal which releases IR into the surroundings
  • only dangerous in high quantities
• visible light

  • the light we use to see
  • wavelength decreases in colours - red, orange, yellow, green, blue, indigo, violet
  • optical fibres - communication through thin glass or plastic that can transmit pulses of lights over long distances - light reflected as it hits the surface - quick data transmitter
  • need specular reflection
• ultraviolet radiation

  • shorter wavelength than visible light, higher frequency
  • sun tan or sunburn - emitted from the sun or sunbeds
  • fluorescence - uv is absorbed and the energy is reemitted as visible light
  • fluorescent lights - generate uv, absorbed by layer of phosphorous which reemits the energy as visible light - energy efficient
  • security - detect forged passports or bank notes
  • sterilise water - destroys microorganisms
• x-rays

  • main use is to view the internal structure of objects - the rays are fired through the persons body, the detector plate records those that get through - rays will be absorbed by dense like bones and pass through non-dense like lungs, pass partially through fleshy parts like heart
  • start off white, turn black where detector plate receives radiation
  • more dangerous for staff than patients - more exposure so wear lead aprons, leave room
• gamma

  • used in medical imaging and to treat cancer
  • sterilise medical equipment - kill microorganisms without causing any other damage
  • sterilise food - kill MO without causing other damage - fresh for longer
  • ionising - damage cells, can lead to cancer, worth risk to treat/detect diseases