WAVES

• A wave is the propagation of energy / information through a medium or vacuum without any transfer of matter. Travelling waves transfer energy, whereas standing waves store it.
• Longitudinal waves are waves in which the oscillations of the particles are parallel to the direction of the wave's travel.
• Transverse waves are waves in which the oscillations of the particles are perpendicular to the direction of the wave's travel.
• Amplitude --> the maximum extent of an oscillation, measured from the equilibrium
• Equilibrium --> the horizontal line that is the midpoint of a wave
• Wave-front --> the point where the wave restarts a "cycle" / all the points on a wave which are in the same phase. E.g. areas of rarefaction / wave crests (but you can choose any point on the wave)
• Frequency --> the number of wave-fronts passing a point per second, it is measured in Hertz (Hz) and the symbol for it is f
• Wavelength --> a wavelength is the distance between two wave-fronts, it is measured in metres (m) and the symbol for it is λ
• Wave period --> the amount of time it takes for two successive wave-fronts to pass a fixed point, it's measured in seconds (s), the symbol for it is T
• Wave speed --> the speed at which a wave travels, it is measured in (m/s), the symbol for it is v

   
• The EM or electromagnetic spectrum is a continuous spectrum of transverse waves which are types of light. Their speed in a vacuum is 3 × 10⁸ m/s or 3 × 10⁵ km/s. Their amplitude is proportionate to the brightness/intensity of the light and their frequency denotes where they sit on the spectrum.
• • Radiowaves --> used for broadcasting and communications
  • Microwaves --> used for cooking, satellite transmissions and Wi-Fi.
  • Infrared --> used for heaters and night vision
  • Visible light --> optical fibres and photography
  • Ultraviolet --> fluorescent lamps and seeing bodily fluids on stuff
  • X-rays --> observing the internal structures of materials and objects, especially for medical purposes
  • Gamma rays --> sterilising food and medical equipment
• • Microwaves --> can heat internal body tissue - prevented by shielding (e.g. metal grids)
  • Infrared --> can cause burns - prevented by heat resistant clothing (e.g. oven gloves and goggles)
  • Visible light --> retinal damage - don't look directly at intense emitters (e.g. The sun or lasers)
  • Ultraviolet --> skin burns or cataracts - wear normal clothing, sunscreen and sunglasses
  • X-rays --> increased cancer risk - lead shielding
  • Gamma rays --> increased cancer risk - standing far away from emitters or several metres of concrete
• An oscilloscope is a machine which graphs soundwaves picked up by a microphone connected to it.
• Sound waves are an example of longitudinal waves. Their speed in air is 343m/s. Their amplitude is directly proportionate to the volume (loudness not capacity) of the sound and their frequency is directly proportionate to the pitch. The range for human hearing is 20-20,000 Hz and as you get older, you lose your ability to hear higher pitched sounds.
• Oscilloscope practical


  1. Set up oscilloscope with two microphones a certain distance from each other

  2. Produce a sound in a straight line with the two microphones

  3. Oscilloscope graphs two sound waves in different colours
• Calculating speed of sound

  1. Calculate difference in time it takes to pick up sound by second mic in seconds (time base × divs between start of wave one and start of wave two × 0.001)

  2. Divide distance between mics in meters by the time it takes for sound to travel between the two
• The oscilloscope should then graph two sound waves in different colours
• Calculate the difference in time it takes to pick up the sound by the second mic in seconds (time base × divs between start of wave one and start of wave two × 0.001)
• Echo practical: this involves setting up about 50 meters away from a smooth wall which will reflect sound with a stopwatch and something that will make sound (e.g. cymbals). Start the stopwatch at the same time you make the first sound and make the sound at the same time as you hear its echo. Time until you have heard 20 echoes. That means the sound has travelled back and forth from the wall (or 100m) 20 times (so 2000m) in a certain amount of time. Divide the number of metres by the number of seconds to get the speed of sound!
• From there you can work out the speed by dividing the distance between the mics in meters by the time it takes for the sound to travel between the two