Waves

Waves

1. Describing waves

   • Wavelength
     • Distance of one point of a wave to the equivalent point on the adjacent wave
   • Frequency
     • No. of complete waves passing a certain point per second
   • Amplitude
     • Maximum displacement of a wave from the undisturbed position
   • Wave equations
     • • v = wave speed
       • f = frequency
       • λ = wavelength
     • wave speed = frequency x wavelength
     • Measuring wave speeds
       • • Wave speed = distance/time

2. Types of waves

   • Transverse waves
     • e.g. light waves
     • Electromagentic spectrum
       • • Transfer energy from one point to another like all other waves
         • Do not require a medium (e.g. particles) to travel, and that is why infrared waves and light travel to Earth from the Sun, despite the lack of air particles in space
         • The shorter the wavelength...
           • ... the higher the fequency
             • ... and the more energy it can transfer to another object when the radiation is absorbed
           • ... the further it can travel through other materials
         • Radio waves
           • Long-wave radio waves
             • Medium-wave radio waves
               • Short-wave radio waves
                 • Very high frequency radio waves
                   • Ultra high frequency radio waves
           • Properties
             • Travel at the speed of light
             • Can be reflected and refracted
           • Uses
             • Used to send terrestrial radio and TV signals
             • Can be produce by oscillations in electrical circuits
               • When current flows through a wire, it produces an electrical field around the wire. When the current changes, the electrical field changes. This changing current produces radio waves. This is how radio transmitters work.
             • The path between the transmitter and receiver must be a straight line with no obstructions such as tall buildings or hills that could be 100m tall
           • Radio waves are refracted in the upper atmosphere (the ionosphere)- the amount of refraction depending on the frequency of the waves
             • The refracted radio waves return to the Earth's surface
             • The longer the wavelength and lower the frequency, the more refraction the waves undergo
             • Microwaves are not refracted or reflected and pass through the ionosphere so are used for satellite communication
         • Microwaves
           • Properties
             • Are radio waves with shorter wavelengths
             • Wavelength varies between 1mm and 30cm
             • Microwaves used for communication have longer wavelengths than those used for cooking because there is less energy associated with mobile phones than with microwave ovens
             • Unlike conventional ovens microwaves do not uses flames or heated metal to cook food- they use microwaves
               • Cook food faster and less expensive to run
               • Microwaves penetrate about 1cm into the outer layers of food before being absorbed
   • Longitudinal waves
     • e.g. sound waves

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