Physics P1

Physics P1

1. Seismic waves

   • P waves
     • Primary
     • Longitudial
     • Go through liquids and solids as they are faster
   • S waves
     • Shear or secondary
     • TranSverse
     • Go through only Solids

2. WAVES

   • Radio waves
     • Communication
       • Large wave length waves diffract around objects allowing them to curve around the earth
       • Short length waves used for FM and TV reflect off the ionosphere and you must be in direct sight of the transmitter to get a signal as they do not diffract.
       • Diffractions is dependant on wave length
       • The short wave length waves hit the ionosphere (a different medium and the top of the wave speeds up therefore reflects the wave back down
       • Lower frequency waves are Transmitted at a lower elevation but refract back down to earth very fast
   • Microwaves
     • Communication
       • Satellite uses microwaves
         • Microwaves are transmitted up to a satellite orbiting the earth which sends the signal back town in a different direction
       • Microwaves are blocked by obstacles so the mast are normally place high in sight of each other
         • Microwaves do not diffract much
       • There is conflicting evidence weather or not microwave mast are bad for your health and microwaves can kill cells in human bodes
     • Cooking
   • Spetrum
     • Radio waves, Microwaves, Infrared, Visible, UV, XRAY, Gamma
   • Velocity = Frequency x wavelength
   • Frequency = The amount of compleat waves to pass a point per second
   • Communicating with light
     • Optical fibres
       • Only {max} 6 reflections
       • Larger than the critical angle meaning it will occur
     • Lasers
       • In phase
         • Coherent
         • Peaks and troughs all line up
         • Same wavelength
       • intense
         • Low divergence
         • Monocromatic
   • The angle of incidence is equal to the angle of reflection
     • Draw the normal first which is at 90 degrees to the mirror
   • Infrared
     • Can be used within remote controls as the monitor could detect and curtain amount of pulses at a curtain speed to mean a command

3. Analogue and digital signals

   • Analogue signals can have loads of different values however ditial only have two value on and off
   • Advantages of digital
     • when travelling signals pick up interference which is amplified in analogue but removed in digital
     • Digital signal can be multiplexed (multiple signals at once)

4. Humans and the enviromemt

   • CFC's reacted with the ozone and cause it to deplete
     • Ozone which normally absorbs UV light is gone
       • UV light hits your skin and causes skin cancer