topic p6- waves

• frequency= no. complete waves passing a certain point each second
• period= time taken for a complete wave to pass a point
• amplitude= maximum displacement of a point on a wave from it's rest position
• wavelength= length of a full cycle of a wave
• wavespeed= speed at which a wave transfers energy, waves transfer energy and can be absorbed, transmitted or reflected
• transverse waves

  • oscillations perpendicular-90 degrees- to direction of energy transfer
  • examples- ripples in water, electromagnetic waves, waves on a string
• longitudinal waves

  • oscillations parallel to direction of energy transfer
  • wavelength, rarefractions, compressions, energy transfer
  • examples- sounds waves- p-waves
• waves on a string

  1. set up experiment shown
  2. adjust the frequency of the signal generator until there's a clear wave on the string
  3. you need to measure the wavelength of these waves
  4. the frequency of the wave is whatever the signal generator is set to
  5. find speed using v=f upside down y
• measure the speed of water ripples using a lamp

  1. using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency
  2. use a lamp to see wave crests on a screen below the tank
  3. the distance between each shadow line is equal to 1 wavelength measure the distance between shadow lines
  4. use v=f times by upside down y to calculate the speed of the waves
• speed of sound

  330m/ s
• Measure speed of sound

  1. Set up the oscilloscope so the detected waves at each microscope as soon as separate
  2. Start with both microphones next to the speaker and slowly move one away until the two waves are aligned on the display
  3. Measure the distance between the microphones to find one wavelength
  4. use v= f times by upside down y to calculate the speed
• All waves can be observed, transmitted or reflected
• You can also explain refraction using wavefront diagrams

  • Less dense to more denser
  • Straight to wonky
• Radio waves, microwaves, infrared visible light ultraviolet x-rays gamma rays

  Frequency increases wavelength decreases
• E M waves are

  • Transverse
  • Travel at the same speed in air or vacuum
  • Transfer energy from source to absorber
  • They are generated due to changes in atoms and their nuclei
• Refraction

  When a wave changes direction as it crosses a boundary between two materials at an angle to the normal
• wave refracts

  • slows down
  • wavelength decreases
  • Bends towards normal
• wave refracts

  • speeds up
  • Wavelength increases
  • Bends away from normal
• What happens to the angle of refraction when light enters a denser medium?

  It decreases compared to the angle of incidence
• remember this:

  
• Radio waves are made by oscillating changes
• radio waves

  1.electrons oscillate and produce EM waves

  2.ac is supplied to the transmitter

  3.emitted radio waves transfer energy from the transmitter to the receiver

  4.ac is produced in the receiver

  5.EM waves are absorbed and cause electrons in the receiver to oscillate
• EM waves are made up of oscillating electric and magnetic fields, the frequency of the waves produced = frequency of the alternating current
• radio waves are mainly used for communication, they are EM radiation with wavelengths longer than about 10cm, e.g. bluetooth, tv, FM radio
• microwaves are used by satellites

  satellite communications and cooking (microwaves)
• infrared radiation

  electric heaters, cooking, infrared cameras
• visible light

  communications through optical fibres
• ultra violet waves

  energy efficient lights and sun tan beds
• x-rays and gamma rays

  medical imaging and medical treatments
• you ca investigate emission with a Leslie cube (metal cube with different surfaces)

  1.place an empty Leslie cube on a heat proof mat and fill with boiled water

  2.hold a thermometer against each side of the cube (they should all be the same)

  3.hold and infrared detector at a set distance away from one of the sides making sure the distance is the same

  5.there should be more IR radiation from the black surface than the white one, and more from the Matt surfaces than the shiny ones

  6.repeat the experiment
• investigating infrared radiation: investigate absorption with melting wax trick:

  -you will need= identical metal plates, Matt black side, silver side, wax + ball bearing

  1.set up with the plates on the outside

  2.sides of plates facing flame each have a diff colour- matt black + silver

  3.ball on black plate falls first as lack absorbs more infrared radiation- transfers more energy to thermal energy store of wax- means wax on black plate melts before wax on silver plate
• radiation dose measure of the risk of harm to body tissues due to exposure to radiation- it is measured in sieverts
• 1 sievert= 1000 millisieverts (msv)
• risk of electromagnetic waves depends on

  -size of dose

  -type of radiation
• ultraviolet (UV) risks

  -can prematurely age skin

  -increases risk of skin cancer
• x-rays + gamma rays risks

  -gene mutation

  -cancer