6 - Waves

• What is the difference between transverse and longitudinal waves?

  - transverse waves have oscillations that move PERPENDICULAR to the direction of energy transfer

  
  

  - longitudinal waves have oscillations that move PARALLEL to the direction of energy transfer

  - ALL longitudinal waves REQUIRE A MEDIUM to travel in, eg. air, a liquid, or a solid
• What is a similarity between transverse and longitudinal waves?

  - it is the wave that travels and not the medium

  - they both transfer energy
• Give an example of a tranverse wave.

  ripples on the surface of water (kinetic energy is transferred)
• Give an example of a longitudinal wave.

  sound waves travelling through air (sound energy is transferred)
• What are the two regions that are showed in longitudinal waves?

  - compressions

  - rarefactions
• What is the 'amplitude' of a wave?

  - the maximum displacement of a point on a wave away from is undisturbed position
• What is the 'wavelength' of a wave?

  
  

  What is the symbol for 'wavelength'?

  
  

  How do we measure the wavelength?


  - the distance from a point on one wave to the equivalent point on the adjacent wave (m)

  
  

  lambda => λ

  
  

  - measure from peak=>peak or compression=>compression
• What is the 'frequency' of a wave?

  - the number of waves passing a point each second (Hz)
• What is the equation for the period of a wave?

  Period = 1/frequency

  
  

  T = 1/f
• What is the 'wave speed'?


  - the speed at which the wave moves through the medium (ie the speed at whcich energy is transferred)
• What is the equation for wave speed?

  speed = frequency x wavelength

  v (m/s) = fλ

  
• What is the method to calculate the speed of sound waves in air?

  
  

  What are some problems with this experiment and how can they be solved?

  1) Two people stand 500m apart.

  2) Person A holds a pair of cymbals and Person B is holds a timer.

  3) Person B starts the timer when they see person A clash the cymbals together and stops timing when they hear the sound.

  4) speed = distance / time taken

  
  

  - every person has a different reaction time; it takes a fraction of a second to press the start/stop button on the timer => have a large number of observers with individual timers & calculate a mean value

  - time between seeing the cymbals clash and hearing the sound is very short => stand apart a larger distance

  
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• What 3 things can happen when a wave hits a boundary that has a different material?

  
  

  What 2 things do these depend on?


  - transmission through material

  - absorption of wave's energy

  - reflection off the surface

  
  

  => depends on the material of the boundary

  => also depends on the wavelength of the wave
• What is the name of the ray that hits the surface of the boundary?

  incident ray
• What is the name of the line that is perpendicular to the mirror line?


  the normal
• What is the law of reflection of all waves?

  the angle of reflection EQUALS the ngle of incidence
• How can we work out where an object will appear in a mirror? (Exam Q)

  - use a ray diagram:

  
  

  1) Draw an incident ray from the object to the mirror.

  2) Draw the normal line at a right angle to the surfacee of the mirror.

  3) Draw the reflected ray.

  4) Remember to draw arrows sowing the direction of both rays.

  5) Draw another incident ray from the object, reflecting off the mirror.

  6) Extend the two reflected rays back into the mirror until they meet at a point.
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• What happens when sound waves travel through solids?

  - they cause vibrations in the solid
• What happens within the ear to cause us to hear a sound?


  - sound waves in the air are funnelled into the ear where they hit the eardrum

  - sound waves cause the eardrum and other parts to vibrate => causes the sensation of sound
• Why is human hearing restricted to sounds below 20Hz or sounds above 20kHz (20,000Hz)?

  - the conversion of sound waves to vibrations of solids only works over a limited frequency range (frequencies outside 20Hz-20kHz may not be able to cause the eardrum to vibrate)
• How do microphones convert wave disturbances between sound waves and vibrations in solids?

  - the cone vibrates when sound waves hit => the microphone then converts these virations to electrical signals
• Why do sound waves travel fastest in solids?

  - the particles in a solid are more dense and closer together => vibrations can be passed on at a faster rate
• Why does the wavelength change when waves pass from one medium to another?

  - the particles are either less dense or more dense in the new medium => the wave speed changes => wave speed is frequency multiplied by wavelength => wavelength also changes
• Explain why the study of seismic waves provides evidence for the structure of the Earth's core. (Exam Q)

  - because S-waves cannot travel through a liquid

  - and S-waves do not travel through the (outer) core