Waves Revision (P6)

Waves Revision (P6)

1. EM Waves

   • Transverse waves
   • They transfer energy from a source to the absorber
   • All EM waves travell at the smae speed through air or the vacuum of space.
     • However they travel at different speeds through different materials
   • EM waves vary in wavelength
     • Large number of frequencies
   • There are 7 basic types and we group them based on wavelength and frequency
   • Our eyes can only detect visible light
   • Because of their different properties EM waves are used for different purposes
   • Uses of EM waves
     • Microwaves are used by satelites
       • TV signals
       • Satellite phones
     • Infrared Radiation can be used to increase or monitor temperature
       • Infrared cameras to detect temperature which turns it into electrical signals
       • Food can be cooked with IR radiation
       • Electrical heaters
     • Fibre optic cables use visible light to transmit data.
       • Work because of reflection. The light rays bounce back and forth
       • Visible light is used because it is easy to refract
     • Ultraviolet Radiation for tanning
       • Overexposure to UV can be dangerous and can lead to types of skin canccers
     • X-rays and gamma rays used in medicine
       • Both rays can be harmful to humans so radiographers wear lead aprons, and stand behind a lead screen.
     • Dangers
       • Some EM Radiation can be harmful to people
       • High frequency waves like UV, and X-ray transfer alot of energy so cause lots of damage
       • UV damages surface cells, which can lead to sunburn and cause skin to age.
         • Some serious side effects are blindness and skin cancer
       • X-rays and Gamma rays are types of ionising radiation.
         • This can cause gene mutation or cell destruction and cancer.

2. Refraction

   • Waves changing direction at a boundary
   • When a wave crosses a boundary of two materials it changes speed
   • If a wave hits the boundary at an angle it changes direction; this is refraction
   • How much it is refracted depends on how much the wave speeds up or slows down
   • The wavelength of the wave changes when it is refracted however the frequency stays the same.
   • The optical density of a material is a measure of how quickly light can travel through it.
     • The higher the optical density , the slower the light waves travel through it
   • Ray diagrams
     • Show the path of waves
     • You can construct a ray diagram for a refracted light ray
     • Rays are straight lines that are perpendicular to wave fronts, they show the direction the direction that the wave is traveling in
   • Wave front Diagrams
     • Explain Refraction using these
     • A line showing all of the points on a wave that are in the same position as each other after a given number of wavelengths
     • When a wave crosses a boundary at an angle , only part of a wave front crosses it at first.
       • If it is traveling into a denser material that part travels slower than the rest of the wave front.

3. Radio waves

   • Made by oscillation charges
   • Mainly used for communication
   • Wavelength no longer than about 10cm
   • Long-wave radio (wavelengths of 1-10km)
     • Transmitted from london to half way around the world (long way)
   • Short wave lengths (wavelengths of about 10m-100m)
     • Bluetooth