Waves

Waves

1. Types of wave

   • Mechanical
     • Longitudinal
       • eg - sound waves
       • moves in parallel to the direction of travel
     • Transverse
       • eg - ripples on a pond
       • moves as right angles to the motion of travel
   • Electromagnetic
     • Radiowaves , microwaves, infrared, visible light, ultraviolet, X - rays, gamma rays
       • Radio waves have highest wavelength, Gamma rays have highest frequency
       • Visible light = red, orange, yellow, green, blue, indigo, violet
     • Radio waves used for communication of information.
     • Microwaves used for heating food, satellite communication and radar. Dangers include heating internal body tissue
     • Infrared is used in heating devices and night vision cameras infrared wavelength from warm objects is longer, than from cool objects. Dangers include burns
     • Visible light is used to see things, in photography and in fibre optics
     • Ultraviolet - used in fluorescent lamps, disco black lights, and for some insects vision. It is responsible for skin cancers and can damage the eyes.
     • X-rays are used to examine internal body structures, to investigate the crystal structures of manufacturing materials, and in radio astronomy (detect rays frim collapsing stars) Can cause sell mutations and cancer
     • Gamma rays are used to treat cancer, and sterilising medical equipment and food products. Can cause cell mutations and cancers

2. Definitions

   • Waves can transfer energy and information from one place to another without transfer of matter
   • Wavelength is the distance between two adjacent points of similar displacement
   • Amplitude is the maximum displacement of a part of the medium from its rest position
   • The period of the wave si the time for one complete cycle of the waveform
   • The frequency of a wave is the number of cycles of the waveform per second
   • Diffraction is the spreading of waves as they pass by the edges of obstacles

3. Equations

   • Frequency = 1 / period
   • wave speed = frequency x wavelength

4. Analogue and digital signals

   • Analogue electrical signals are continuously variable voltages
   • Digital electrical signals can have either of only 2 possible values (typically 5V and 0V), representing 1 and 0 in the binary system
   • Signals lose energy as they are transmitted so need to be amplified. This means interference the signal has picked up is also amplified meaning the sound quality decreases. Digital signals can be regenerated, both amplifying and restoring their original 0 and 1 shape, virtually eliminating unwanted interference.

5. Light

   • Reflection
     • angle of incidence = angle of reflection
     • Angles measured are between the normal and the ray
   • forming an image in a mirror
   • Refraction
     • the bending of light when it travels from one medium to another
     • When light enters a glass block it bends towards the normal, and when it leaves it bends away from the normal
     • The degree of bending depends on the material the light is traveling into
       • refractive index = sin I / sin r
     • Total Internal reflection
       • refractive index = 1 / sin c (c is the critical angle)
       • When light hits the medium at an angle greater than the critical angle, all the waves reflect back into the glass

6. Sound

   • Longitudinal wave
   • Humans can detect from 20Hz to 20kHz
   • Echoes are sound waves reflecting
   • The pitch of a sound depends on the frequency
   • The loudness depends on the amplitude

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