Lecture 1 Waves and Sounds (Ch 16) Principles of

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Lecture 1 Waves and Sounds (Ch 16) Principles of Powered By Docstoc
					           Lecture 1:

   Waves and Sounds (Ch 16)
                 &
Principles of Linear Superposition
    and Interference (Ch 17)
            01-30-2007
                  Nature of Waves

    Transverse Wave                 Longitudinal Wave




Radio waves, Light, Microwaves   Sound
Periodic Waves
                           Speed of a Wave




Example 2: Transverse waves travel on the strings of an electric guitar after the strings
are plucked (see Figure 16.9). The length of each string between its two fixed ends is
0.628 m, and the mass is 0.208 g for the highest pitched E string and 3.32 g for the
lowest pitched E string. Each string is under a tension of 226 N. Find the speeds of the
waves on the two strings.
   Mathematical Description of a Wave


                                                                        Phase Angle




These equations apply to transverse or longitudinal waves and assume that
y = 0 m when x = 0 m and t = 0 s.




The quantity x/v is the time needed for the wave to travel the distance x.
          Nature of Sound Waves
Sound Waves are LONGITUDINAL WAVES
                   Nature of Sound Waves
                            Frequency of Sound wave
                            Each cycle of a sound wave includes one
                            condensation and one rarefaction, and the frequency
                            is the number of cycles per second that passes by a
                            given location.

                            A sound with a single frequency is called a pure tone.




Sound can be generated whose frequency lies below 20 Hz or
above 20 kHz, although humans normally do not hear it.
Sound waves with frequencies below 20 Hz are said to be
infrasonic, while those with frequencies above 20 kHz are referred
to as ultrasonic.

Pitch: A pure tone with large frequency is a high pitched sound
              Nature of Sound Waves
Pressure Amplitude of Sound Wave




Loudness depends on the amplitude of the wave.
                         Speed of Sound

                                     Bad = Adiabatic Bulk Modulus

                                     Y = Youngs Modulus




Air (0 deg) = 330 m/s
Air (20 deg) = 343 m/s

Mercury = 1450 m/s

Steel = 5960 m/s
                         Sound Intensity


                                                               (
                                                               1
                                                               6
                                                               .
                                                               8
                                                               )
The unit of sound intensity is power per unit area, or W/m2.
                               Decibels

The decibel (dB) is a measurement unit used when comparing two sound intensities.


                                                                                (
                                                                                1
                                                                                6
                                                                                .
                                                                                1
                                                                                0
                     •Threshold of hearing = 0 dB                               )
                     •Normal Conversation = 65 dB

                     •Inside Car = 80 dB

                     •Live rock Concert = 100dB

                     •Pain = 130 dB
Doppler Effect
                  Doppler Effect


                                   (
                                   1
                                   6
                                   .
MOVING OBSERVER                    1
                                   5
                                   )
                     Linear Superposition
THE PRINCIPLE OF LINEAR SUPERPOSITION
When two or more waves are present simultaneously at the same place, the resultant
disturbance is the sum of the disturbances from the individual waves.
                             Diffraction




Single Slit: First Minimum = Sinθ = λ/D
Beats
                Transverse Standing Wave




Total Length,
Speed of waves traveling on a string
Longitudinal Standing Wave