Waves

Waves

1. Terms

   • Amplitude - the height of a wave from its undisturbed position
   • Wavelength - the distance between the same point on two adjacent waves
   • Frequency - the number of complete wavs passing through a point in a second, measured in Hertz
     • You can use this to find the period of a wave, which is the time it takes for a wave to complete a full cycle
       • T=1/F
   • Wave speed- speed at which energy is transferred
     • Wave speed = frequency x wavelength

2. Types of Waves

   • Transverse
     • All waves are perpendicular to the direction of energy transfer
     • Most common type of wave
   • Longitudinal
     • Oscillations are parallel to the energy transfer
     • Has refractions, where the waves are not compressed

3. Wave behaviour

   • When a wave meets a boundary between 2 materials it does one of three things
     • Absorbed - energy is transferred to the materials store, mainky thermal energy
     • Transmitted - the wave travels through the material refracting on the other side
     • Reflected - the wave is sent back away from the second material

4. Electromagnetic waves

   • Vibrate through electric and magnetic waves
     • For this reason they can travel through a vacuum as they dont require particles
   • They travel at different speeds, ranging from 10^15m to 10^4m, but all come together to form a spectrum
     • Raging Martians Invade Venus Using X-ray Guns
       • Radio, Microwave, Infrared, Visible light, Ultra Violet, X-Rays,Gamma

5. Refractions

   • When a wave crosses a boundary it changes speed
     • If it speeds up it bends away from the normal
     • If it slows down, it bends towards the normal
     • The frequency never changes
   • If the wave hits the boundary, it changes angle and speed
     • If the wave hits at the normal, it only changes speed
   • Optical density is how quickly light can travel through a material
     • In most cases, the higher the density, the slower the wave travels

6. Radio Waves

   • Long wave radio lengths diffract (bend) over surfaces, so can travel to a receiver even when it is not in sight
   • Short wave radio lengths reflect from the ionosphere which is an electrically charged surface on the Earths upper atmosphere. They have a shorter range
   • Medium wave radio lengths do the same as short, but only during certain times of the day

7. Microwaves

   • Different uses
     • Microwaves have to travel through Earths watery atmosphere to reach satellites
       • Microwaves are transmitted from Earth to a satellite, and then transmitted back to Earth. Due to the long distance, there is often a time delay
     • Microwaves are also used to heat food
       • The microwaves penetrate deep into the food and transfer energy to water molecules which heats them up
         • The water molecules then transfer energy to the rest of the food, in turn heating it up

8. Infrared

   • Every object gives off Infrared radiation , the hotter the object, the more IRR it gives off
   • IR cameras can detect IRR and turns it into an electric signal. The brighter the image, the hotter it is
   • Absorbing IRR causes objects to heat up
   • Electric heaters has a wire that heats up when a current flows through it. It emits IRR which is transferred to the rooms thermal energy stores, warming the room up

9. UV radiation

   • Fluorescence is a property of certain chemicals, where UV radiation is absorbed and visible light is emitted
     • Fluorescent lights generate UV radiation, which s absorbed and re-emitted as visible light by a layer of phosphorous on the inside of the bul
   • UV radiation is emitted by the sun and gives people a tan
     • Over exposure can be dangerous

10. X Ray and Gamma Rays

    • X Rays can pass through flesh but not bones, as they are desnser
      • What you see is the radiation that is absorbed/not absorbed
    • X Rays and Gamma rays can be used to kill cells, so we use them to kill cancerous cells
      • Gamma rays are emitted and followed by a medical tracer.
    • The use of these rays can be dangerous, so people in the vicinity wear lead aprons