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Waves

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Ch 11 # 45 Types of Waves Longitudinal: The medium oscillates in the same direction as the wave is moving Sound ... of Waves on a string Example: guitar ... – PowerPoint PPT presentation

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Title: Waves


1
Waves
2
Types of Waves
8
3
Period and Velocity
22
4
Slinky Question
  • Suppose that a longitudinal wave moves along a
    Slinky at a speed of 5 m/s. Does one coil of the
    slinky move through a distance of five meters in
    one second?
  • 1. Yes
  • 2. No

12
5
Harmonic Waves
Wavelength The distance ? between identical
points on the wave.
Amplitude The maximum displacement A of a point
on the wave.
Angular Frequency w w 2 p f
Wave Number k k 2 p / l
Recall f v / l
y
x
20
6
Example microwave
  • The wavelength of microwaves generated by a
    microwave oven is about 3 cm. At what frequency
    do these waves cause the water molecules in your
    burrito to vibrate ?

The speed of light is c 3x108 m/s
29
7
Interference and Superposition
  • When too waves overlap, the amplitudes add.
  • Constructive increases amplitude
  • l2-l1 m ?
  • Destructive decreases amplitude
  • l2-l1 (m1/2) ?

34
8
Example two speakers
  • Two speakers are separated by a distance of 5m
    and are producing a monotone sound with a
    wavelength of 3m. Other than in the middle,
    where can you stand between the speakers and hear
    constructive interference?

9
Example two speakers
  • Two speakers are separated by a distance of 5m
    and are producing a monotone sound with a
    wavelength of 3m. Where can you stand between the
    speakers and hear destructive interference?

10
Reflection Act
  • A slinky is connected to a wall at one end. A
    pulse travels to the right, hits the wall and is
    reflected back to the left. The reflected wave is
  • A) Inverted B) Upright
  • Fixed boundary reflected wave inverted
  • Free boundary reflected wave upright

37
11
Standing Waves Fixed Endpoints
  • Fundamental n1
  • ln 2L/n
  • fn n v / (2L)

44
12
Velocity of Waves on a string
µ mass per unit length of string As µ
increases, v decreases, f decreases (? fixed)
17
13
Example guitar
A guitars E-string has a length of 65 cm and is
stretched to a tension of 82N. If it vibrates
with a fundamental frequency of 329.63 Hz, what
is the mass of the string?
48
14
Summary
  • Wave Types
  • Transverse (eg pulse on string, water)
  • Longitudinal (sound, slinky)
  • Harmonic
  • y(x,t) A cos(wt kx) or A sin(wt kx)
  • Superposition
  • Just add amplitudes
  • Reflection (fixed point inverts wave)
  • Standing Waves (fixed ends)
  • ln 2L/n
  • fn n v / 2L

50
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