6.1 Waves in Air, Fluids and Solids

• Two types of waves

  • Transverse
  • Longitudinal
• Transverse wave


  A wave for which the oscillations are perpendicular to the direction of energy transfer
• Longitudinal wave


  A wave for which the oscillations are parallel to the direction of energy transfer and requires a medium to travel in eg. air, a liquid or a solid.
• Transverse waves

  • Electromagnetic waves
  • Seismic s-waves
  • ripples on a water surface
• Longitudinal waves

  • Sound waves
  • Seismic p-waves
• Two parts of a longitudinal wave

  • Compressions
  • Rarefactions
• Amplitude


  The maximum displacement of a point on a wave from its undisturbed position
• Wavelength


  The distance from a point on a wave to the same position on the adjacent wave; most commonly peak to peak or trough to trough
• Frequency


  The number of waves that pass a given point each second
• Unit used for frequency

  Hertz, Hz
• Wave speed

  The speed at which the wave moves or at which energy is transferred through a medium
• Equation for wave speed

  Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)
• Units for wave speed equation

  v  = f  λ
• Sound waves travel through a solid


  The particles in the solid vibrate and transfer kinetic energy through the material
• Frequency range of human hearing

  • 20 Hz - 20kHz
• Ultrasound waves

  Waves which have a frequency higher than the upper limit of human hearing (20kHz)
• Uses for ultrasound waves

  • Medical imaging
  • Industrial imaging
• Seismic waves are produced by
• Types of seismic waves

  • P-waves
  • S-waves
• Echo sounding


  A technique used to detect objects in deep water and measure water depth
• Echo sounding process

  1. High frequency sound waves emitted

  2. Reflected

  3. Detected
• Time difference between emission and detection, alongside wave speed, are used to calculate distances
• Evidence using a slinky


  Both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels. The water molecule/ air particle doesn't move as the wave travels through.
• Label the Wavelength...

  A) Peak

  B) Amplitude

  C) Wavelength

  D) Trough

  E) Wavelength

  F) Wavelength

  G) Rest position

  
• The period is the time (in seconds) for one wave to pass a point.
• period(s) = 1 /frequency(Hz)

  T = 1/f
• a method to measure the speed of sound waves in air

  Person A is holding cymbals and 500m adjacent is Person B who is holding a timer. Person B starts the timer when they see that Person B has clashed the cymbals but then stops the timer when they hear the sound of the cymbals clashing.
• a method to measure the speed of sound waves in air

  Calculate the speed of the sound waves but dividing the distance travelled by the time taken.

  v=d/t
• Problems with this experiment.


  ➡People have different reaction time

  ➡It takes a fraction of a second between hearing the sound and stopping the timer aswell as seeing the cymbals and starting the timer.
• Reducing this error of reaction time


  ➡having a large amount of observers - taking all their results are discarding any anomalies calculating a mean value.
• Problems with this experiment 2


  ➡The time between seeing the cymbals clash and hearing the sound is very short. - making it very difficult to press the timer at the correct times.
• Reducing this error of pressing the timer at the right time


  ➡increasing the distance between Person A and Person B as the longer the distance the longer the time making it easier to start and stop the timer at the correct times.
• Waves can be absorbed or transmitted at the boundary between two different materials.

  Th energy of the wave could be absorbed by the material. Wave may not pass through material at all.

  The wave may simply be reflected off the surface of the material
• The surface of a material can transmit absorb or reflect a wave depending on material and wavelength of the wave.
• The angle of reflection equals the angle of incidence.
• ➡Normal is 90 degress of Mirror

  ➡Reflected Ray is 90 degrees of Incident Ray

  A) Incident ray

  B) Plane Mirror

  C) Normal

  D) Angle of reflection

  E) Angle of Incidence

  F) Reflected ray

  
• Specular reflection


  Reflection from a smooth, flat surface is called specular reflection. This is the type of reflection that happens with a flat mirror. The image in a mirror is:

  • upright
  • virtual
• Specular reflection


  Image.

  A) Reflected Rays 1 & 2

  B) Incident Ray 1 &2

  
• Diffuse reflection

  If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.

  
• Sound waves are longitudinal waves. They cause particles to vibrate parallel to the direction of wave travel. The vibrations can travel through solids, liquids or gases. The speed of sound depends on the medium through which it is travelling