# Waves - PowerPoint PPT Presentation

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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