chapter 8 waves— sound and light a wiggle in time wave: a wiggle in space and time—a disturbance...
TRANSCRIPT
Chapter 8
WAVES—SOUND AND LIGHT
∗ 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
In this unit, we will look at:
I can define what a wave is, list several different types of waves and compare a wave with a vibration.
Learning Goal:
Vibration:
a wiggle in time
Wave:
a wiggle in space and time—a disturbance that travels from one place to another transporting energy.
Vibrations and Waves
∗ http://sunshine.chpc.utah.edu/labs/waves/wave_basics/waves.htm
Wave Demonstration
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
A. 1/20 second.
B. 20 seconds.
C. more than 20 seconds.
D. none of the above.
If the frequency of a particular wave is 20 Hz, its period is
Vibrations and Waves
CHECK YOUR NEIGHBOR
A. 1/20 second.
Explanation:
Note when ƒ = 20 Hz, T = 1/ƒ = 1/(20 Hz) = 1/20 second.
If the frequency of a particular wave is 20 Hz, its period is
Vibrations and Waves
CHECK YOUR ANSWER
• The propagation of a disturbancethrough 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
A. frequency.
B. period.
C. wavelength.
D. amplitude.
The distance between adjacent peaks in the direction of travel for a transverse wave is its
Wave Motion
CHECK YOUR NEIGHBOR
C. wavelength.
Explanation:
The wavelength is the distance between any adjacent identical parts of the waveform.
The distance between adjacent peaks in the direction of travel for a transverse wave is its
Wave Motion
CHECK YOUR ANSWER
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
Wave Motion
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
A. along the wave.
B. perpendicular to the wave.
C. both of the above.
D. neither of the above.
The vibrations along a transverse wave move in a direction
Transverse and Longitudinal Waves
CHECK YOUR NEIGHBOR
B. perpendicular to the wave.
Comment:
The vibrations in a longitudinal wave, in contrast, are along (or parallel to) the direction of wave travel.
The vibrations along a transverse wave move in a direction
Transverse and Longitudinal Waves
CHECK YOUR ANSWER
I can define what a wave is, list several different types of waves and compare a wave with a vibration.
Learning Goal:
End Day 1
Sound Waves
Homework Review
I can calculate wave properties in terms of frequency, wavelength, wave speed, and amplitude.
Learning Goal:
∗ http://www.youtube.com/watch?v=cK2-6cgqgYA
Sound and Waves
End of Day 2
Waves and Light
I can calculate wave properties in terms of frequency, wavelength, wave speed, and amplitude.
Previous Learning Goal:
A. 1/20 Hertz.
B. 20 Hertz.
C. more than 20 Hertz.
D. none of the above.
If a wave machine is generating a wave by making 20 vibrations per second, the frequency is
Wave Review
A. 1/20 Hertz.
B. 20 Hertz.
C. more than 20 Hertz.
D. none of the above.
If a wave machine is generating a wave by making 20 vibrations per second, the frequency is
Wave Review
For this wave, the wavelength is shown by:
A
B
C
Any of the lines
Wave Review
A
B
C
For this wave, the wavelength is shown by:
A
B
C
Any of the lines
Wave Review
A
B
C
Wave Review
A. 30 cm/second.
B. 1 cm/second.
C. 100 cm/second.
D. Can’t determine with the information given.
For a wave with a frequency of 10 Hertz, a period of 1/10 seconds, a wavelength of 10 cm and an amplitude of 3 cm, the wave speed would be:
Wave Review
A. 30 cm/second.
B. 1 cm/second.
C. 100 cm/second.
D. Can’t determine with the information given.
For a wave with a frequency of 10 Hertz, a period of 1/10 seconds, a wavelength of 10 cm and an amplitude of 3 cm, the wave speed would be:
Wave speed =
frequency x
wavelength
For this wave, the amplitude is shown by:
A
B
C
Any of the lines
Wave Review
A
B
C
For this wave, the amplitude is shown by:
A
B
C
Any of the lines
Wave Review
A
B
C
Homework Review
I can explain the nature of light in terms of wavelength and the electromagnetic spectrum.
Learning Goal:
Light:
Electromagnetic waves
created by vibrating
electric charges having
frequencies that fall
within the range of sight
The Nature of Light
Light:
the frequency of vibrating electrons equals the frequency of the light
The Nature of Light
Light:
Travels nearly a million times faster than sound in air
Light can travel through a vacuum!
The Nature of Light
Light:
Light and all electromagnetic waves are transverse waves
The Nature of Light
Energy
The Electromagnetic Spectrum
The Nature of Light
A. radio waves.
B. microwaves.
C. visible light.
D. gamma rays.
The electromagnetic spectrum is a span of electromagnetic waves, ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of
The Nature of Light
CHECK YOUR NEIGHBOR
C. visible light.
Explanation:
This can be inferred by a careful study of the spectrum.
The smallest portion of the electromagnetic spectrum is that of
The Nature of Light
CHECK YOUR ANSWER
Electromagnetic waves are composed of perpendicular electric and magnetic fields that vibrate perpendicular to the direction of wave travel.
The Nature of Light
A photographer wishes to photograph a lightning bolt by setting his camera so that it is triggered by the sound of thunder.
The Nature of Light
A situation to ponder�
A. Good idea for nearby lightning strikes.
B. Good idea for all strikes.
C. Poor idea for nearby lightning strikes.
D. Poor idea for all strikes.
Is this a good idea or a poor idea?
A situation to ponder�
CHECK YOUR NEIGHBOR
D. Poor idea for all strikes.
Explanation:
Light travels about a million times faster than sound. By the time the sound of thunder arrives, the lightning bolt is long gone.
Is this a good idea or a poor idea?
A situation to ponder�
CHECK YOUR ANSWER
Reflection:
the returning of a wave to the medium through which it came when encountering a reflective surface
Reflection
Law of reflection:
angle of incidence = angle of reflection
Reflection
Diffuse Reflection
When light is incident on a rough surface, it is reflected in many directions.
Reflection
A. Wet surface is smooth with less diffuse reflection, part of which would otherwise reach the driver’s eyes.
B. Wet road usually means a wet windshield.
C. Wet road usually means more vapor in the air.
D. There is no reason—that’s just the way it is.
Compared with a dry road, seeing is difficult when driving at night on a wet road. Why?
Reflection
CHECK YOUR NEIGHBOR
A. Wet surface is smooth with less diffuse reflection, part of which would otherwise reach the driver’s eyes.
Compared with a dry road, seeing is difficult when driving at night on a wet road. Why?
Reflection
CHECK YOUR ANSWER
Transparent materials:
(glass and water)
Light passes through in straight lines, with atoms undergoing a series of absorptions and reemissions
Transparent and Opaque Materials
Opaque materials:
colored glass is opaque to much of incident white light
Transparent and Opaque Materials
I can explain the nature of light in terms of wavelength and the electromagnetic spectrum.
Learning Goal:
End of Day 3
Waves and Light
Color
I can explain the nature of light in terms of wavelength and the electromagnetic spectrum.
Learning Goal:
The Electromagnetic Spectrum
The Nature of Light
The color we see depends on frequency of light ranging from lowest (red) to highest (violet). In between are colors of the rainbow.
Color
High
Frequency
Low
Frequency
Hues in seven colors: Red, Orange, Yellow, Green, Blue, Indigo, and Violet.
Grouped together, they add to appear white.
Color
Selective Reflection
Most objects don’t emit light, but reflect light.
Color
Selective Reflection
A material may absorb some of the light and reflect the rest.
Examples:Paint
Nature
Color
Selective Reflection
Dependent on the wavelengths present in the light.
Color
Color
CHECK YOUR NEIGHBOR
Green “G” is reflected
because it is not absorbed
so Green is seen
Red “R” is reflected
because it is not absorbed
so Red is seen
Selective Transmission
The color of a transparent object depends on the color of the light it transmits (or lets pass through).
Color
Three types of cone receptors in our eyes perceive color—each is stimulated by only certain frequencies of light:
• Light of lower frequencies stimulates the cones sensitive to low frequencies (red)
• Light of middle frequencies stimulates the cones sensitive to mid-frequencies (green)
• Light of high frequencies stimulates the cones sensitive to high frequencies (blue)
Vision & Color
Stimulation of all three cones equally, we see white light
Vision & Color
Additive primary colors (red, blue, green):
red + blue = magenta
red + green = yellow
blue + green = cyan
Color
Opposites of primary colors:
opposite of green is magenta
opposite of red is cyan
opposite of blue is yellow
The addition of any color to its opposite color results in white.
Color
Color
RedGreen
Blue
Magenta Cyan
Yellow
White
A. Infrared radiation.
B. Ultraviolet radiation.
C. Both A and B.
D. Neither A nor B.
To which is the human eye blind?
Color
CHECK YOUR NEIGHBOR
A. Infrared radiation.
B. Ultraviolet radiation.
C. Both A and B.
D. Neither A nor B.
To which is the human eye blind?
Color
CHECK YOUR ANSWER
In a vacuum (like space), all electromagnetic waves travel at the same speed:
3.0 x 108 m/sec.
This is called the Speed of Light and its symbol is c.
c = frequency x wavelength
Speed of Light
In a vacuum (like space), all electromagnetic waves travel at the same speed:
3.0 x 108 m/sec.
This is called the Speed of Light and its symbol is c.
c = frequency x wavelength
Speed of Light
The different colors of light that we see correspond to different frequencies.
The frequency of red light is lower than the frequency of blue light.
Because the speed of both kinds of light is the same, a lower frequency wave has a longer wavelength. A higher frequency wave has a shorter wavelength.
Therefore, red light’s wavelength is longer than blue light’s.
Speed of Light
Color
CHECK YOUR NEIGHBOR
Yellow light has a longer wavelength than
green light. Which color of light has the higher
frequency?
A. Yellow.
B. Green.
C. Both have the same wavelength.
Color
CHECK YOUR NEIGHBOR
Yellow light has a longer wavelength than
green light. Which color of light has the higher
frequency?
A. Yellow.
B. Green.
C. Both have the same wavelength.
A wave with a longer wavelength
has lower frequency!
I can explain the nature of light in terms of wavelength and the electromagnetic spectrum.
Learning Goal:
End of Day 4
Properties of Waves and
Wave Behavior
I can explain the difference between refraction, diffraction and interferencein terms of wave behavior.
Learning Goal:
Occurs whenever successive impulses are applied to a vibrating object in rhythm with its natural frequency.
Resonance
http://www.youtube.com/watch?v=m686UO68AXI
Resonance
http://www.youtube.com/watch?v=m686UO68AXI
http://academic.greensboroday.org/~regesterj/potl/Waves/DiffractionInterference/
StandingWave.htm
Refraction:
the bending of a wave due to a change in themedium and/or speed of the wave
Refraction
Refraction occurs when sound waves are affected by uneven winds, or when air near the ground is warmer than air above.
Refraction
Converging lens (a)-
incoming parallel light rays refract and converge to a focal point
Diverging lens (b)-
incoming parallel light rays refract in such a way that extended rays diverge to a focal point in front of the lens
Refraction - Lenses
Reflection:
the returning of a wave to the medium through which it came when encountering a reflective surface
Reflection
Any bending of light by means other than reflection and refraction
Smaller openings produce greater bending of the waves at edges
Diffraction
Amount of diffraction depends on thewavelength of the wave compared to the size of the obstruction that casts the shadow
Diffraction
http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.htm
Diffraction
Interference
is the combined effect of two or more overlapping waves.
Interference
Two types of interference:
Constructive interference
crest of one wave overlaps crest of another wave ⇒ individual effects add, resulting in a wave of increased amplitude
Interference
Two types of interference:
Destructive interference
crest of one wave overlaps the trough of another ⇒individual effects are reduced
Interference
A. sound.
B. light.
C. both of these.
D. neither of these.
Interference is a property of
Interference
CHECK YOUR NEIGHBOR
A. sound.
B. light.
C. both of these.
D. neither of these.
Interference is a property of
Interference
CHECK YOUR ANSWER
End of Day 5
Doppler Effect and Wave-Particle Duality
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
Two overlapping waves
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
Small opening causes wave to bend
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
Two media – Air and Water
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
A. Interference.
B. Reflection.
C. Refraction.
D. Diffraction.
Two media – air and prism
This shows an example of:
Wave Behavior Review
CHECK YOURSELF
Wave Behavior Review
The Doppler Effect:
a change in frequency as measured by an observer due to the motion of the
• source or
• listener
Named after Austrian physicist and mathematician, Christian Johann Doppler
The Doppler Effect
∗ http://www.youtube.com/watch?v=O5rqMPdQMQ8&playnext=1&list=PL3E17B10CA65C1234&feature=results_main
∗ http://www.youtube.com/watch?v=iN3fO5l4Rww
∗ http://www.youtube.com/watch?v=m3MkZjlacaI
Example of Doppler Effect:
The frequency of waves received by an observer increases as a sound source moves toward the observer.
The Doppler Effect
The wave frequency decreases as the source moves
away.
A. speed of its sound increases.
B. frequency of sound increases.
C. wavelength of its sound increases.
D. all increase.
When a fire engine approaches you, the
The Doppler Effect
CHECK YOUR NEIGHBOR
A. speed of its sound increases.
B. frequency of sound increases.
C. wavelength of its sound increases.
D. all increase.
Comment:
Be sure you distinguish between sound, speed, and sound frequency.
When a fire engine approaches you, the
The Doppler Effect
CHECK YOUR ANSWER
A. sound.
B. light.
C. both A and B.
D. neither A nor B.
The Doppler effect occurs for
The Doppler Effect
CHECK YOUR NEIGHBOR
A. sound.
B. light.
C. both A and B.
D. neither A nor B.
Explanation:
Astronomers measure the spin rates of stars by the Doppler effect.
The Doppler effect occurs for
The Doppler Effect
CHECK YOUR ANSWER
Is Light a Wave or a Particle?
In ancient times, Plato, other Greek philosophers, and Isaac Newton thought that light was composed of tiny particles.
100 years after Newton, Thomas Young demonstrated the wave nature of light with interference experiments.
The Wave–Particle Duality
25 years later, the wave view was confirmed by Heinrich Hertz.
Later in 1905, Albert Einstein challenged the wave theory and stated that light was confined in tiny particles of energy called photons. His particle model of light was verified by the photoelectric effect.
The Wave–Particle Duality
Today, light is acknowledged to have both a wave nature and a particle nature—
Wave–Particle duality:
• light reveals itself as a wave or particle depending on how it is being observed
• light behaves as a wave when traveling from a source to a place where it is detected and behaves as a stream of photons when it interacts with a detector
The Wave–Particle Duality
The Photoelectric Effect
When light shines on certain metal
surfaces, electrons are ejected
from those surfaces.
Ultraviolet and violet light impart
sufficient energy to knock
electrons from those metal
surfaces while lower-frequency
light does not, even when very
bright.
The Wave–Particle Duality
A. The red light in a dark room is usually too dim.
B. Red light has insufficient energy per photon to “expose” the film.
C. Red light is low-temperature light.
D. None of the above.
Why is unexposed black and white photographic film not “exposed” when in red light, but is when in white light?
The Wave–Particle Duality
CHECK YOUR NEIGHBOR
A. The red light in a dark room is usually too dim.
B. Red light has insufficient energy per photon to “expose” the film.
C. Red light is low-temperature light.
D. None of the above.
Why is unexposed black and white photographic film not “exposed” when in red light, but is when in white light?
The Wave–Particle Duality
CHECK YOUR ANSWER
Findings:
1. ejection of electrons depended only on the frequency of light
2. the higher the frequency of the light, the greater the kinetic energy of ejected electrons
Explanation:
Electrons in the metal are bombarded by “particles of light”—photons. The energy of each photon is proportional to its frequency: E ∼ ƒ.
The Wave–Particle Duality
A. wave.
B. particle.
C. both of the above.
D. none of the above.
Light travels as a wave and is absorbed as a
The Wave–Particle Duality
CHECK YOUR NEIGHBOR
A. wave.
B. particle.
C. both of the above.
D. none of the above.
Explanation:Light is wavelike as it travels but particle-like when it encounters a surface.
Light travels as a wave and is absorbed as a
The Wave–Particle Duality
CHECK YOUR ANSWER
∗ Why is the sky blue?
∗ http://www.youtube.com/watch?v=8vUzS9b_0IE
Other Topics
∗ http://www.youtube.com/watch?v=hip-4KF6z4o
∗ http://www.youtube.com/watch?v=HpovwbPGEoo
Ruben’s Tube
∗ http://www.youtube.com/watch?v=4DlqVuNMydk
∗ http://www.youtube.com/watch?v=VBmKtsxpoZA
Tidal Waves And Tsunami
∗ http://dsc.discovery.com/tv-shows/curiosity/videos/withstanding-a-rogue-wave.htm
Rogue Waves
∗ http://dsc.discovery.com/tv-shows/curiosity/videos/lifes-biggest-questions.htm
Space and Light