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WAVES

How are waves generated?

Waves are generated by

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Wave—a disturbance that transmits energy through empty space or through a medium

Medium—any solid, liquid, or gas

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Types of Waves 1. Electromagnetic—consists of oscillating electric and

magnetic fields

a. Requires no medium

b. Ex: light, X-rays, radio, gamma rays

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Types of Waves 2. Mechanical—energy transferred from one particle

of a medium to the next

a. Medium required

b. Ex: sound, water waves

c. 2 types: transverse & longitudinal

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Wave Topics A. Period (p. 516)

B. Frequency (p. 516)

C. Wave Speed (p. 518-521)

D. Transverse Waves (p. 511)

E. Longitudinal Waves (p. 512)

F. The Parts of a Wave (p. 512, 514-515)

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What type of mechanical wave

is this? TRANSVERSE

Transverse Wave Wave moves perpendicular to the particles of the

medium

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TROUGH

CREST

WAVELENGTH

AMPLITUDE

Transverse Wave

What type of mechanical wave

is this?

Animation

http://www.kettering.edu/physics/drussell/Demos/waves/wavemotion.html

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Longitudinal Wave Wave moves parallel to the particles of the medium

http://www.kettering.edu/physics/drussell/Demos/waves/wavemotion.html

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Longitudinal Wave

COMPRESSION RAREFACTION

WAVELENGTH

Longitudinal Wave

Frequency

• # of waves/time

• Hertz (Hz)

Period

• time/wave

• Seconds (s)

1

f T

Wave Speed Depends on the medium

Wave speed = frequency x wavelength

v

f l

v: velocity (m/s)

f: frequency (Hz)

l: wavelength (m)

T: period

l

v T

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What are two types of

mechanical waves?

Longitudinal

Transverse

Review What are the key parts of the following wave?

What are the appropriate units for frequency?

Frequency is the number of waves that pass a point each second. It is measured in Hertz (Hz).

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Wave Sample Problems

Calculate the speed of waves in a puddle that are 0.650 m apart and made by tapping the water surface 5 times each second.

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Wave Sample Problems Crickets produce a chirping sound based on the outside temperature. Some

chirps can have wavelengths in air of 1.25 m. If the speed of sound in air is 346 m/s, what is the frequency of the chirp produced by a cricket?

What is its wave period?

Wave Sample Problems A manatee can typically hear sounds with frequencies up to 32,000 Hz.

What is the speed of sound in water if a wave with this frequency has a wavelength of 10 cm. (Hint: Convert cm to meters.)

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Wave Sample Problems

A buoy bobs up and down in the ocean. The waves have a wavelength of 6.3 m, and they pass the buoy at a speed of 12.8 m/s. What is the frequency of the waves?

How much time does it take for one wave to pass under the buoy ? (Hint: Find the wave period.)

Wave Practice Problems, Part 2 check your answers

3) 0.0076 m

4) 10 s

5) 0.0136 m

6) 38 m

7) 1.6 m/s

8) 129 Hz

0.0078 s

9) 15000 m/s

10) 1.6 Hz

0.625 s

Review

What are the key parts of the following wave?

What is the appropriate unit for wave period?

Wave period is the amount of time it takes for one wave to pass a given point. It is measured in seconds (s).

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1. Quiz Review 2. Group Review

Game

A wave is disturbance that transmits ________

____________ waves consists of oscillating electric and magnetic fields and do not require a _________. Examples include ______________________.

___________ waves must have a medium because the energy is transferred from through the particles. There are two types of this wave __________ and ________.

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ENERGY

ELECTROMAGNETIC

MEDIUM

ALL FORMS AND COLORS OF LIGHT

MECHANICAL

LONGITUDINAL

TRANSVERSE

TROUGH

CREST

WAVELENGTH

AMPLITUDE

The time it takes for one wave to pass a point is called _______________

The number of waves that pass in one second is called ______________

These variables are reciprocals (inverse) of each other. T= 1/F or F= 1/T

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WAVE PERIOD (T)

FREQUENCY (F)

AFTER THE QUIZ WAVE BEHAVIORS GUIDED READING

Electromagnetic Spectrum

The Electromagnetic

Spectrum

• Vibrating magnetic & electric fields

• Can travel through a vacuum

• v = 3.00 x 108 m/s (in a vacuum)

Electromagnetic Waves

The Electromagnetic Spectrum

Radio Waves

• Lowest frequency

• Longest wavelength

• Radios, TVs, cell phones

Microwaves

• Used in cooking (microwave oven)

• Food absorbs wave

• Energy from wave converts to heat

Infrared

• “heat waves”

• Uses: keeping food

warm, animal tracking,

infrared photography

http://coolcosmos.ipac.caltech.edu/image_galleries/our_ir_world_gallery.html

Visible Light

• Different frequencies seen as different

colors

• ROYGBIV

• Red: lowest frequency, least energy

• Violet: highest frequency, most energy

Ultraviolet

• Higher frequency than light

• More penetrable

• Causes sunburns, damages tissue, kills

bacteria

X-Rays

• High energy

• Can penetrate soft tissue

• Uses: medical tests, checking luggage at

airport

Gamma Rays

• High frequency, short wavelength

• High energy

• Produced by nuclear particles

• Used in radiation treatment to kill cancer

cells

Draw a transverse wave and label the amplitude.

• Wave Behaviors Discussion

• Wave Behaviors lab

• Lab Explanations

Wave Behaviors

Reflection

Refraction

Diffraction

Interference

Wave Behaviors

Reflection

– Bounces off boundary

Refraction

– The bending of a wave as it moves from one medium to another

Diffraction

– The bending of a wave around a barrier

Reflection

Refraction

Diffraction

Interference

The combining of 2 waves

Two types:

– Constructive

– Destructive

Constructive Interference

Destructive Interference

Destructive Interference

Waves with different amplitudes

Standing Waves

Result from interference between a

wave and its reflected wave.

http://id.mind.net/~zona/mstm/physics/waves/standingWaves/understandingSWDi

a1/UnderstandingSWDia1.html

http://www.walter-fendt.de/ph14e/stwaverefl.htm

Node Antinode

refraction

Destructive interference

diffraction

reflection

Light & Wave Behaviors Lab

• When light passes

through a series of

tiny slits or grooves

called a diffraction

grating, light fans

out from each slit.

White light is

spread out into a

spectrum

according to

wavelength.

Refraction

• Pouring water in the

cup causes the light

to refract at a different

angle. This is why

the penny is no

longer in view when

looking at it from the

original viewing

angle.

• Light waves bounce

off the inner and outer

layers of the nail

polish film. At times

the waves interfere

constructively to

produce certain colors

and destructively to

produce other colors.

• You could see the

image of each other

when the angles

were the same. The

law of reflection

states that the angle

of incidence equals

the angle of

reflection.

How is amplitude altered during constructive/destructive interference?

• Constructive interference results a combined wave with a larger amplitude than the separate waves.

• Destructive interference results in a combined wave with a smaller amplitude than the separate waves.

• Wave Behaviors Discussion

• Wave Behaviors lab

• Lab Explanations

Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.

Constructive Interference

Amplitude = 7 cm

How are frequency and pitch of a sound wave altered as sound moves away from you?

• Sound Notes and Video Clips

• Resonance

• Speed of Sound & Sonic Boom

• Doppler Effect

Sound travels as a longitudinal wave

Sound waves are created by vibrations.

FREQUENCY

• Frequency is known as Pitch in sound waves

• Human hearing: 20 Hz to 20,000 Hz

• Infrasonic: <20 Hz

• Ultrasonic: >20,000 Hz

AMPLITUDE

• Amplitude is known as Loudness in

sound waves

• Loudness measured in decibels (dB)

Near total silence—0 dB

A whisper - 15 dB

Normal conversation - 60 dB

A lawnmower - 90 dB

A car horn - 110 dB

A rock concert or a jet engine - 120 dB

A gunshot or firecracker - 140 dB

More Sound Terminology…

• Natural Frequency is the frequency at

which an object naturally vibrates

• Resonance occurs when an outside

vibration matches the natural frequency

of an object causing it to vibrate

VELOCITY

• The speed of a sound wave depends on:

1. The type of Medium

• Fastest in solids

2. The Temperature of the medium

• Faster in warmer temps

Other Scenarios of Doppler

Effect • Object is traveling at the speed of sound

Other Scenarios of Doppler

Effect

• Object is traveling faster than the

speed of sound

• Creates sonic booms

Pitch and the Doppler Effect

Wavelength and Frequency Review

• As the wavelength increases, the

frequency ___________________.

• This means wavelength and frequency are

indirectly proportional.

• Which of these waves has the higher

frequency?

decreases

This one! It has the smaller wavelength.

Frequency and Sound

• Frequency = pitch

• Pitch—the highness or lowness of a sound

High frequency: high pitch Low frequency: low pitch

DOPPLER EFFECT

• The perceived change in frequency (pitch)

due to the motion of either the source of

the wave and/or the observer

How does it happen?

As a sound is created, the sound waves spread out in all directions around the source.

Then What?

If the source moves, the wave

becomes bunched up on one side and

more spread out on the other.

Doppler Effect

Lower pitch; longer wavelength

Lower frequency

Higher pitch; shorter wavelength

Higher frequency

If the sound is moving away from you . . .

If the sound is moving towards you . . .

So, what does that mean?

If the source is moving

towards you, the pitch sounds higher.

And if the source is

moving away from you, the pitch sounds

lower.

http://www.youtube.com/watch?v=-d9A2oq1N38

http://www.youtube.com/watch?v=gWGLAAYdbbc

http://www.youtube.com/watch?v=ofESdVdX-fY

http://www.youtube.com/watch?v=z0EaoilzgGE

http://youtu.be/h4OnBYrbCjY

http://youtu.be/sH7XSX10QkM

Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.

Constructive Interference

Amplitude = 7 cm

How are frequency and pitch of a sound wave altered as sound moves away from you?

Frequency will decrease as the sound moves away from you causing the pitch to seem lower.

• Sound Notes and Video Clips

• Resonance

• Speed of Sound & Sonic Boom

• Doppler Effect

REVIEW

Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.

Destructive Interference

Amplitude = 3 cm

Echoes are examples of what wave behavior?

Reflections

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1. Review of EM Spectrum 2. Wave Test Review

The Electromagnetic Spectrum

Question & Answer

Which EM wave has the longest wavelength, thus the lowest amount of energy?

Radio

Which EM wave is the only one that can be seen by the human eye?

Visible

Light

Which EM wave is shorter than radio waves, but longer than infrared?

Microwaves

Which EM wave aids in photosynthesis and provides vitamin D to people?

Ultraviolet

Which EM wave has the most energy and is the most intense and dangerous?

Gamma

Which EM wave is used at the airport to “see” through suitcases and bags?

X-rays

Which EM wave is the heat given off by objects?

Infrared

Conclusion

Electromagnetic Waves:

Can travel in a vacuum

Speed of all EM waves is

3.0 x 108 m/s in a vacuum

Slows down in gas, slower in liquids, slowest in solids

Review

BR: Classify this wave behavior.

Refraction

How is this different from Diffraction?

Refraction is the bending of a wave due as it enters a new medium, but diffraction is the bending of a wave around an obstacle or opening.

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REVIEW Which wave behavior caused this glass to

break?

Resonance

What are the basic properties of sound?

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1. Wave Stations 2. QR Code Questions

Sound Lab Summary

Pay close attention as we discuss some

of the things you say in the lab

activities. You will use this

information to explain how each

activity worked.

Sounds are produced by

vibrations.

Sound waves are LONGITUDINAL.

Frequency = Pitch

The shorter the wavelength, the

higher the pitch.

Humans can hear between 20

Hertz (infrasonic) and 20,000

Hertz (ultrasonic)

http://www.ultrasonic-ringtones.com/

Natural Frequency

All objects produce their

own unique frequency

and sound (timbre)

Resonance

When a sound matches

the natural frequency of

an object causing it to

vibrate

Amplitude = Loudness

Constructive interference

creates louder sounds

Media

Sound travels best (and

fastest) through solids

Sound cannot travel through

empty space

1. _______ creates louder sounds.

* constructive interference B. destructive interference C. diffraction

2. All objects produce their own unique

frequency and sound called ____.

A. resonance B. natural pitch * natural frequency

3. The longer the wavelength the

_____ the pitch?

A. longer B. higher * lower

4. When a sound matches the natural

frequency of an object causing it to

vibrate * resonance B. natural frequency C. tone

5. Sound travels best (and fastest)

through

A. gases * solids C. liquids

6. Sounds less than 20 Hz are

A. supersonic B. ultrasonic * infrasonic

REVIEW Which wave behavior caused this glass to break?

Resonance

What are the basic properties of sound?

Sound travels as a longitudinal wave and can experience many different wave behaviors: resonance, constructive/destructive interference, resonance, frequency/amplitude changes.

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1. Wave Stations 2. QR Code Questions