Sound

1
Sound light

• 7/18/2008

2
Sound

• Sound as a mechanical wave
• A wave is a disturbance that travels through a
  medium, transporting energy from one location to
  another location
• Sound as a longitudinal wave
• Longitudinal waves are waves in which the motion
  of the individual particles of the medium is in a
  direction which is parallel to the direction of
  energy transport

3
Wavelength and Frequency
http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/s
ound/soundtoc.html

• Sound as a pressure wave
• Speed of travel wavelength frequency

4
Interference
http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/s
ound/soundtoc.html

• Wave interference is the phenomenon which occurs
  when two waves meet while traveling along the
  same medium. The interference of waves causes the
  medium to take on a shape which results from the
  net effect of the two individual waves upon the
  particles of the medium.

http//www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/
waves/ipl.html
5
Nodes and Anti-nodes

• locations along the medium where constructive
  interference continually occurs are known as
  anti-nodes
• locations along the medium where destructive
  interference continually occurs are known as nodes

6
Doppler effect

• The Doppler effect can be described as the effect
  produced by a moving source of waves in which
  there is an apparent upward shift in frequency
  for the observer and the source are approaching
  and an apparent downward shift in frequency when
  the observer and the source is receding.

http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/s
ound/soundtoc.html
7
Reflection, diffraction refraction

• Reflection of sound waves off surfaces can lead
  to one of two phenomenon - an echo or a
  reverberation
• Refraction of waves involves a change in the
  direction of waves as they pass from one medium
  to another.
• Diffraction involves a change in direction of
  waves as they pass through an opening or around a
  barrier in their path.

8
Natural Frequency

• The frequency or frequencies at which an object
  tends to vibrate with when hit, struck, plucked,
  strummed or somehow disturbed is known as the
  natural frequency of the object.

9
Guitar string standing wave
http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/s
ound/soundtoc.html
10
Standing wave

• a standing wave pattern was described as a
  vibrational pattern created within a medium when
  the vibrational frequency of a source causes
  reflected waves from one end of the medium to
  interfere with incident waves from the source
• specific points along the medium appear to be
  standing still while other points vibrated back
  and forth

11
Standing wave

• Such patterns are only created within the medium
  at specific frequencies of vibration. These
  frequencies are known as harmonic frequencies or
  merely harmonics. At any frequency other than a
  harmonic frequency, the interference of reflected
  and incident waves results in a disturbance of
  the medium which is irregular and non-repeating.

12
Light as a wave

• Light behaves both as a wave and as a particle
• Evidence for wave-like behavior
• Doppler effect
• Interference, reflection refraction like any
  other wave
• Diffract when the dimensions of the obstacle are
  smaller than the wavelength of the wave

13
Interference for light

• Red dots constructive interference
• Blue dots destructive interference

http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
ight/u12l1b.html
14
Youngs experiment(evidence that light is a wave)
http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
ight/lighttoc.html
15
Youngs experiment(evidence that light is a wave)

• Monochromatic light (light of a single color, of
  the same frequency) must be used.
• Coherent light must be used.
• - Two light waves are vibrating in phase i.e.
  the crest of one wave must be produced at the
  same precise time as the crest of the second wave

16
Path difference

• Antinodal Points
• - PD m ? where m 0, 1, 2, 3, 4, ...
• Nodal Points
• PD m ? where m 0.5, 1.5, 2.5, 3.5, ...
• http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
  ight/u12l3b.html

http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
ight/u12l3b.html
17
Equation to determine wavelength(?)

• ? y d / (m L)
• Where
• - L is the distance from slits to screen
• y is the distance from central fringe to the
  fringe in analysis
• m is the order value
• d is the slit separation

18
Equation to determine wavelength(?)

• Big Assumption is yltltltL
• Assume S1P BP, then S2P - S1P S2B , which is
  the PD
• Assume angle BS1S2 angle PAC
• Assume ? is a small angle, sin(?) PD / d
  tangent(?) y / L
• ? y d / (m L)

http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
ight/u12l3c.html
19
Light as a particle

• Wave-particle duality
• waveparticle duality is the concept that all
  matter exhibits both wave-like and particle-like
  properties
• Photoelectric effect (evidence that light is a
  particle)
• where h is Planck's constant (6.626 10-34 J
  seconds). Only photons of a high-enough
  frequency, (above a certain threshold value)
  could knock an electron free.

20
Wave-particle duality

• Louis-Victor de Broglie formulated the de Broglie
  hypothesis, claiming that all matter, not just
  light, has a wave-like nature he related
  wavelength (denoted as ?), and momentum (denoted
  as p)

21
Electron diffraction

• Evidence that matter with large mass can behave
  like a wave
• transmission electron microscope (TEM), or a
  scanning electron microscope (SEM) as electron
  backscatter diffraction
• the electrons are accelerated by an electrostatic
  potential in order to gain the desired energy and
  determine their wavelength before they interact
  with the sample to be studied.

22
Electron diffraction

• The electrons are accelerated in an electric
  potential U to the desired velocity
• m0 is the mass of the electron, and e is the
  elementary charge. The electron wavelength is
  then given by

23
Electron diffraction

• An SEM may typically operate at an accelerating
  potential of 10,000 volts (10 kV) giving an
  electron velocity approximately 20 of the speed
  of light
• A typical TEM can operate at 200 kV raising the
  electron velocity to 70 the speed of light. We
  therefore need to take relativistic effects into
  account.

24
Reference

• http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/l
  ight/lighttoc.html
• http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/s
  ound/soundtoc.html
• http//en.wikipedia.org/wiki/Wave-particle_duality