Chapter 8
WAVES—
SOUND AND LIGHT
In this unit, we will look at:
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Vibrations and Waves
Wave Motion
Transverse and Longitudinal Waves
The Nature of Sound
Resonance
The Nature of Light
Reflection
Transparent and Opaque Materials
Color
Refraction
Diffraction
Interference
The Doppler Effect
The Wave–Particle Duality
Learning Goal:
I can define what a wave is,
list several different types
of waves and compare a
wave with a vibration.
Vibrations and Waves
Vibration:
a wiggle in time
Wave:
a wiggle in space and time—a
disturbance that travels from one
place to another transporting
energy.
Wave Demonstration
∗ http://sunshine.chpc.utah.edu/labs/waves/w
ave_basics/waves.htm
Vibrations and Waves
Description:
• Vibration
in terms of frequency (time)—how
often vibration motion occurs
• Wave
in terms of its frequency, speed,
amplitude, and wavelength
Vibrations and Waves
Frequency:
number of to-and-fro vibrations in a given
time
Unit: 1 vibration per second = 1 Hertz
Period:
defined as the time it takes for a complete
vibration
Unit: any unit of time, usually seconds
Vibrations and Waves
Relationship between frequency and period:
Frequency = 1/period Unit: Hertz (Hz)
Period = 1/frequency Unit: second (s)
The source of all waves is a vibration.
Vibrations and Waves
CHECK YOUR NEIGHBOR
If the frequency of a particular wave is
20 Hz, its period is
A. 1/20 second.
B. 20 seconds.
C. more than 20 seconds.
D. none of the above.
Vibrations and Waves
CHECK YOUR ANSWER
If the frequency of a particular wave is
20 Hz, its period is
A.
1/
20
second.
Explanation:
Note when ƒ = 20 Hz, T = 1/ƒ = 1/(20 Hz)
= 1/20 second.
Wave Motion
• The propagation of a disturbance
through a medium
• The medium transporting the wave
returns to initial condition after
disturbance has passed
• Requires an energy source and a
medium (except for light) through
which the energy is transferred
Wave Motion
Wave characteristics:
Crest—highest point Trough—lowest point
Wavelength
Amplitude
Frequency
Period
Wave Motion
CHECK YOUR NEIGHBOR
The distance between adjacent peaks
in the direction of travel for a
transverse wave is its
A.
B.
C.
D.
frequency.
period.
wavelength.
amplitude.
Wave Motion
CHECK YOUR ANSWER
The distance between adjacent peaks
in the direction of travel for a
transverse wave is its
C. wavelength.
Explanation:
The wavelength is the distance between
any adjacent identical parts of the
waveform.
Wave Motion
Wave speed:
• describes how fast the disturbance
moves through the medium
• related to frequency and wavelength
Equation for wave speed:
Wave speed = frequency × wavelength
v = ƒλ
Transverse and Longitudinal
Waves
Two different types of waves classified in the
direction in which the medium vibrates
compared to the direction of energy travel:
• Longitudinal wave: the vibration is in the
direction of travel.
• Transverse wave: the vibration is in right
angles (sideways) to wave travel.
Transverse and Longitudinal
Waves
Longitudinal wave
Transverse wave
Transverse and Longitudinal Waves
CHECK YOUR NEIGHBOR
The vibrations along a transverse wave
move in a direction
A.
B.
C.
D.
along the wave.
perpendicular to the wave.
both of the above.
neither of the above.
Transverse and Longitudinal Waves
CHECK YOUR ANSWER
The vibrations along a transverse wave
move in a direction
B.
perpendicular to the wave.
Comment:
The vibrations in a longitudinal wave, in
contrast, are along (or parallel to) the
direction of wave travel.
Learning Goal:
I can define what a wave is,
list several different types
of waves and compare a
wave with a vibration.
End Day 1