chapter 8 waves— sound and light a wiggle in time wave: a wiggle in space and time—a disturbance...

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


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


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.


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


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


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


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


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


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.


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

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

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?


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?


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


Learning Goal:

End of Day 3

Waves and Light

Color


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


A material may absorb some of the light and reflect the rest.

Examples:Paint

Nature

Color


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

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!


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



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.

Small opening causes wave to bend



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.

Two media – Air and Water



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.



CHECK YOURSELF

A. Interference.

B. Reflection.

C. Refraction.

D. Diffraction.

Two media – air and prism



CHECK YOURSELF

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.


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 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.


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?


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?


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.


A. wave.

B. particle.



Light travels as a wave and is absorbed as a


CHECK YOUR NEIGHBOR

A. wave.

B. particle.



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


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

chapter 8 waves— sound and light a wiggle in time wave: a wiggle in space and time—a disturbance...

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