Waves #1

Waves #1

1. The Basics

   • Wavelength - distance from one peak to the next
   • Frequency - how many complete waves per second
   • Amplitude - height of the wave
   • Speed - how fast the wave goes
   • Period - time taken for one complete wave
   • Speed = frequency x wavelength
   • 1 kHz = 1000Hz, 1 MHz = 1000000Hz
   • Wave shape
     • Transverse
       • e.g. light, water ripples
       • vibrations at 90 degrees to the direction energy is transferred by the wave
     • Longitudinal
       • e.g. sound, shock waves
       • Vibrations are along the same direction as the wave transfers energy

2. Wave Behaviour

   • Wavefronts are imaginary planes that cut across all waves, connecting points in adjacent waves which vibrate together
   • The distance between each wavefront is equal to one wavelength
   • The Doppler Effect
     • The waves produced by a source which is moving towards or away from an observer will appear to have a different wavelength than they would if the source were stationary
     • The frequency of a source moving TOWARDS you will seem HIGHER and its wavelength will seem SHORTER
       • The faster a wave is moving away from you, the longer it will appear
     • The frequency of a source moving AWAY from you will seem LOWER and its wavelength will seem LONGER
   • Electromagnetic waves
     • Radio waves - smallest frequency, largest wavelength
     • Gamma rays - largest frequency, smallest wavelength
     • Order: Radio, micro, infra-red, visible, ultra-violet, x-rays, gamma rays

3. Uses of Electromagnetic Waves

   • Radio waves
     • ✓ TV and FM broadcasting
       • ✗ cancer
   • Microwaves
     • ✓ cooking
       • ✗ internal heating of body tissue
   • Infrared
     • ✓night-vision equipment, heaters
       • ✗ skin burn and eye damage
   • Visible light
     • ✓ Optical fibres, photography
       • ✗ burns and blindness
   • UV lights
     • ✓ Fluorescent things
       • ✗ damage cells and blindness
   • X-Ray
     • ✓ Medical imaging
       • ✗ mutations/cancer
   • Gamma rays
     • ✓ Sterilising food
       • ✗ cell mutation, tissue damage, cancer

4. Sound Waves

   • Sound waves are longitudinal waves caused by vibrations
   • Human ear can hear sounds with frequencies between 20Hz and 20 000Hz
   • The denser the medium, the faster sound travels through it
     • Travels faster in liquids than in gases
   • Reflected by hard, flat surfaces
   • Sound waves refract as they enter different media
     • As they enter denser material, they speed up
   • Oscilloscope
     • An oscilloscope is a device that graphically displays the wave shape of an electrical signal
     • The greater the amplitude of a wave, the more energy it carries
       • This means it'll be louder
     • The higher the frequency, the higher the pitch
       • Frequency is measured in Hz
         • The more complete cycles displayed on the screen, the higher the frequency
     • high frequency = high pitched, low frequency = low pitch