Physics 1b

Physics 1b

1. Waves

   • Types of waves
     • Longitudinal Waves
       • Examples
         • Sound Waves
         • Shock waves
         • Ultrasound
           • Higher frequency humans can hear
         • Slinky pushed
       • Vibrations are parallel to direction of energy transfer
     • Transverse waves
       • What most waves are.
       • Examples
         • Light
         • EM Waves
         • Waves on string
         • Slinky wiggled up and down
       • Vibrations are perpendicular to energy transfer
   • Reflection, Refraction and Diffraction
     • Reflection
       • Bouncing of waves
       • What allows us to see things
     • Refraction
       • When a wave goes through a new object (medium), refraction changes its direction
       • Only occurs if wave meets new medium at an angle
       • If wave meets a new medium on the normal line (straight on), speed will change but direction won't.
     • Diffraction
       • All waves can diffract
       • Spreading out of waves, from waves bending around object
   • Equations
     • Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
   • Amplitude, Wavelength, Frequency
     • Amplitude
       • Is the displacement from the rest position (middle line) to the crest (peak)
       • NOT, from a trough to a crest
     • Wavelength
       • The length of a full cycle of the wave
       • eg. From crest to crest
     • Frequency
       • Number of complete waves passing a certain point per second
       • OR number of waves produced by a source each second
       • Measured in hertz (Hz)
       • 1Hz = 1 wave per second

2. Electromagnetic Spectrum (EMS)

   • Waves vary in wavelength
   • All EM waves travel the same speed in a vacuum
   • Higher frequency = Shorter wavelength
   • Types of Waves
     • Radio Waves
       • Don't need to be in line of sight
       • Used for TV and Radio
     • Microwaves
       • Use Satellites
       • Used for calls
       • Used for cooking
         • Some wavelengths are absorbed by water and heats up
     • Infrared Radiation
       • Used for remote controls
       • Optical Fibres
         • Thin high quality glass strands in cable casing
         • Used in phone lines
         • Carry data fast and far
         • Use infrared and visible waves
     • Visible Light
     • Ultraviolet
     • X-rays
     • Gamma Waves
   • Great song to learn on YT

3. Sound

   • Vibrating objects
   • Sound is a LONGITUDINAL WAVE
   • Travels faster in solid than liquid, and faster in liquid than solid
     • Because of amounts and space between particles
   • Can't travel in space, no particles
   • Reflect and Refract
     • Echo
       • Reflected sound waves
     • Sound waves reflect by hard flat surfaces
     • Can refract - change direction
   • Frequency
     • High frequency = higher pitch
     • Lower Frequency = Lower pitch
     • Frequency = number of complete vibrations per second 100Hz = 100 vibrations
     • Higher pitch also means shorter wavelength
     • Loudness = Amplitude

4. Origin Of The Universe

   • Universe seems to be expanding
     • Galaxies seem to be moving away from each other
   • Doppler Effect
     • Happens in Longitudinal and Transverse waves
     • Eg. 'vroom' a car engine sound a lower pitch when its passed and is moving away
   • Big Bang
     • Scientists detected lower frequency EM radiation from all parts of the universe
       • In microwave part of EM spectrum
       • Called CMBR = Cosmic Microwave Background Radiation
     • Only theory that explains CMBR
     • Massive explosion
     • Might not be true
       • Predicts that expansion should slow, but it is speeding up
   • Red-shift = shifting towards red end of spectrum
     • More distant galaxies have greater red shift than nearer galaxies
       • Means universe is expanding
     • When objects move away from us, its light waves are stretched into lower frequencies or longer wavelengths

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