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Waves

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Waves & Sound Objectives Describe the measurable properties of waves and explain the relationships among them and how these properties change when the wave moves from ... – PowerPoint PPT presentation

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Title: Waves


1
Waves Sound
2
Objectives
  • Describe the measurable properties of waves and
    explain the relationships among them and how
    these properties change when the wave moves from
    one medium to another.
  • Qualitatively describe the shift in frequency in
    sound or electromagnetic waves due to the
    relative motion of a source or a receiver.

3
Chapters 2526
  • Waves are periodic disturbances that propagate
    through a medium or space
  • a medium does not travel with the wave
  • Mechanical waves require a medium
  • Electromagnetic waves do not require a medium

4
More on waves
  • Longitudinal waves particles of the medium move
    parallel to the direction of the wave

Sound is an example of this type of wave.
5
Transverse Waves
  • Transverse waves displacement of the particles
    of the medium are perpendicular to the direction
    of propagation of the wave.

6
Phase of a wave
7
Frequency
8
Properties of Waves
  • 1. Rectilinear propagation advancement of a
    wave is perpendicular to the wave front
  • 2. Reflection waves bounce off barriers and
    rebound in opposite direction
  • Law of reflection
  • Incident angle reflected angle (i r)
  • 3. Refraction bending (changing direction) of a
    wave as it travels from one medium into another

9
More properties
  • 4. Diffraction spreading of a wave as it passes
    beyond the edge of a barrier
  • http//www.physicsclassroom.com/Class/waves/U10L3b
    .html
  • 5. Interference result of 2 or more waves
    passing through the same medium at the same time

http//www.physicsclassroom.com/Class/waves/U10L3c
.html
10
Math associated with waves
  • Frequency 1 / Period (f 1/T)
  • Period 1 / Freqency
  • i.e., f 60cycles per second 60 hz 60/s
  • Also v f l
  • where velocity frequency x wavelength

11
Sound Waves
12
Math re waves
  • I P/A Intensity Power/Area
  • Units watt / cm2
  • Intensity relates to loudness

You are 1 km away from a radio tower, what is the
intensity of the signal of a 100,000 kw radio
station? 1 km 105 cm 100,000 kw 100,000,000w
108 w I P/A 100,000 kw / 4 p (105)2 7.96 x
10-7 w/cm2
13
More math
  • b 10 log I
  • Io 10-16 w/cm 2
  • b, Intensity level
  • I, Intensity
  • Io, threshhold of hearing
  • We all dont hear the same, so this is a
    comparative measurement, in decibels

14
Flow chart for b (intensity) problems
  • If I 4.7 x 10-10 w/cm2
  • 10xlog(4.7 2nd EE -10 / 1 2nd EE -16) 66.7
    dB
  • If I 2.9 x 10-3 w/cm2
  • 10xlog(2.9 2nd EE -3 / 1 2nd EE -16) 135
    dB

15
Now we are going backwards from intensity level
(dB) to intensity (w/cm2)
  • If the intensity level is 83 dB, convert that to
    intensity in w/cm2.
  • B 10 log I / Io get to a working eqtn
  • B /10 log I / Io
  • Log-1(B/10) Log-1(log I/Io)
  • Log-1(B/10) I/Io

16
More to come
  • Doppler Effect is the apparent change in
    frequency as a result of relative motion between
    the source of a sound and an observer.

F o f s v v o v v
s
fo, frequency heard by observer fs, frequency of
source v, velocity of sound in air vo, velocity
of observer vs, velocity of source
17
More on Doppler
  • Stationary observer
  • Observer moving away v-vs on bottom
  • Observer moving toward vvs on bottom
  • Stationary source
  • Observer moving toward vvo on top
  • Observer moving away v-vo on top
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