# Lecture 1 Waves and Sounds (Ch 16) Principles of

Document Sample

```					           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

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

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

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 9 posted: 7/30/2010 language: English pages: 19