Waves, Sound, and EM Spectrum

Waves, EM Spectrum and Sound

• Describe how energy is transferred through sound waves and how pitch and loudness are related to wave properties of frequency and amplitude.

An Introduction to Waves

• Waves: repeated disturbances in a medium (substance) that transfers energy through it

• Medium: the material the wave travels through (air, water, etc)

Water Tuning fork

2 Main Types of Waves:

• Transverse wave: The matter moves up and down as the wave travels horizontally

• Compressional (Longitudinal) wave: Matter and wave move horizontally

Which is which?

TRAVIS the (transverse wave) Caterpillar

Transverse Waves

Draw this picture of a Transverse Wave:

• Fancy words for your wave: – Crest: highest point– Trough: lowest point– Wavelength (λ): length from crest to crest (or

trough to trough)

– Frequency (f): number of wavelengths that pass a point each second A.k.a. pitch

• (1 Hertz = 1 wavelength per second)– Period: amount of time it takes one wavelength to

pass a point– Amplitude: measure from equilibrium position to

top of crest or bottom of trough. A.k.a. loudness

How do you measure wavelength and frequency?

How do you measure wavelength and frequency?

WORK ON: Waves WS

Compressional Waves

Draw this picture of a Compressional Wave:

(More terms? Yaaaaaay!!!)

Compression and Rarefaction

Compression Rarefaction

• Wavelength (λ): From compression to compression (or expansion to expansion)

• Frequency (f): number of wavelengths that pass a point each second

• Period: amount of time it takes one wavelength to pass a point

• Amplitude: more compressed it is, the more amplitude (loudness) it has

Amplitude in Transverse vs Compression Waves

Where is the crest? Trough?

What pattern do you notice between wavelength and frequency?

As wavelength increases, frequency ______

As frequency increases, wavelength ______

What is wavelength?What is frequency?

https://www.youtube.com/watch?v=Xu6hbS2TLSw

Relationship btw Frequency and Wavelength (watch the volume)

https://www.youtube.com/watch?v=HVmt1DQWalQ

Think of your own comparison:

• A transverse wave is like ___________

• A compression wave is like ___________

• Using a slinky, how can you show a transverse wave and a compressional wave?

Pitch and Loudness

• Sound Intensity:

– more energy = more intensity

– more distance from source = less intensity

• Discuss: Which of the above waves has high intensity?

• Loudness (decibel or dB): how the ear and brain understands sound intensity.

How the brain interprets sound waves

• http://www.educationscotland.gov.uk/resources/s/sound/amplitude.asp

• Pitch: how the ear and brain understand frequency (or wavelength) – (high pitch of a mosquito vs low pitch of a tuba)

– Humans can hear sounds from 20 Hz to 20,000 Hz.– (Dogs: up to 35,000Hz……Bats: up to 100,000 Hz)– What is the relationship between pitch and

frequency?

Pipe Cleaner Wave Models

Create a Wave…

Table 1 & 3: Transverse, High freq, low amp

Table 4 &6: Compressional, high freq, high amp

Table 5 &7: Transverse, low freq, low amp

Table 2 & 8: Compressional, low freq, high amp

Line up by…

1) Frequency

2) Amplitude

3) Loudness

4) Pitch

4 corners: soft sound, loud sound, high pitch, low pitch

Waves Lab #1

Slinkies/Snakies

• Slinky and Snaky (helical spring) used to ask many questions about waves (4 minutes):

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

Sound

• Sound waves = Compressional Waves (a.k.a.

Longitudinal Waves) in the medium of air

Compression Compression Compression Compression

JUST THINK:What would sound waves “look” like? (3 min)

http://www.youtube.com/watch?v=_vYYqRVi8vY

What happens in soft sounds?

What happens in loud sounds?

Does air itself travel when a sound wave passes through it?

Higher frequency means _______ pitch sound.

Discuss:• Which of the above are waves?• Which of the above are sound waves?• Which of the above waves are heard as

LOUDER in your ear?• Which of the above waves has a higher pitch?

Doppler Effect and Red Shift

• Doppler Effect: a change in pitch that is due to a moving source– Moving towards you increases frequency (pitch)– Moving away from you decreases frequency (pitch)

HOW DOES THE SOUND CHANGE AS IT PASSES YOU?

• When is the motorcycle pitch high?

• When is the motorcycle pitch low?

• What does a high pitch wavelength look like?

• What does a low pitch wavelength look like?

• How can a tuning fork show that sound compresses air?

• How can a tuning fork be used to show the Doppler Effect?

Car moving to the right

Tuning Fork Evidence:

• How does the action of a tuning fork that is struck and placed in water show evidence that sound pushes air and travels in waves?

• How does a tuning fork that is rapidly moved (closer-further-closer-further) from your ear show the Doppler Effect?

Redshift• the Doppler Effect on light emitted from

moving planets!

• When planets move away from you, the wavelength gets longer and more RED!!

• When planets move towards you, the wavelength gets shorter and more BLUE!!

Questions for the Doppler Video

1) How many sounds does a tuning fork make?

2) Why did the sound change as he moved it?

3) How many sounds does the “football” make?

4) Why did the sound change as he moved it?

Questions about Redshift Video

1) Why does the plane’s sound change as it moves through the air?

2) Why are objects coming towards the Earth blueshifted?

3) Why are objects moving away from the Earth redshifted?

4) How does redshift give evidence for the big bang?

• *Video with Doppler Effect Demos (3 min)*:

http://www.youtube.com/watch?v=JX_A99Bq9AI

• *Explains Doppler and Red shift (3 min)*

http://www.youtube.com/watch?v=FhfnqboacV0

• Explains Red Shift and Big Bang (3 min)

http://www.youtube.com/watch?v=y5tKC3nEx2I&list=PLJ215MiUVBbOYu7uX91e8sUO40oKgDHO8&feature=c4-overview-vl

WAVE WAR!

Each person will have a partner. Your pair will pair up with another pair.

You will:

• Create questions

• Exchange with another pair

• Answer

• Discuss right answers with question creators

Battle 1: Wave Parts

1. Each pair draw 2 waves on graph paper.

2. Write 3 questions about your waves including at least 3 of the following vocabulary words:

• Amplitude• Frequency• Pitch• Loudness• Wavelength• Crest/Trough/Equilibrium Point• Compressional Wave• Transverse Wave

Battle 2: SoundEach pair creates 5 questions on sound including at

least 3 of the following vocabulary words:• Transverse wave• Compressional Wave• Compression/Rarefaction• Amplitude• Loudness• Frequency• Pitch• Medium for Sound• Doppler Effect

Electricity and Magnetism

• Describe the properties and uses of forms of electromagnetic radiation from radio frequencies through gamma radiation. For example: Compare the energy of microwaves and X-rays.

The Electromagnetic Spectrum:

Electromagnetic waves

• Electr = ? • Magnetic = ?

• Electromagnetic waves:

– Like other waves: They transfer energy

– Unlike other waves: Do not need medium to move through, can move through space! (a vacuum)!

Properties and Uses of EM Waves• Radio: radio, microphone to speaker, radar,

(size range: length of football field to human)

• Microwaves: microwave

(size: bumblebee to pin head)

• Infrared: thermal (a.k.a. heat!) energy

(size: Cell to bacteria)

(“EM Waves are everywhere!” cont.)•Visible Light: the only part of the spectrum we can see

•Ultraviolet: in sunlight (helps make vitamin D! Also makes skin cancer and cataracts)

•X-rays: X-rays of broken bones, radiation therapy (size of an atom)

•Gamma Rays: radiation therapy (size of a nucleus)

Please record the following:

• SPEED DATING Review game

• Waves, Sound, EM Spectrum Quiz

• Introductional Video about EM waves by NASA (5:20 min):

http://www.youtube.com/watch?v=cfXzwh3KadE

Do When Quiz is Complete1. Turn in any missing work. (Most haven’t turned

in the following assignment.)

a. On a piece of graph paper Draw three transverse waves of your choice. For Each wave:

b. Label (Crest, wavelength, amplitude, trough)

c. Write a sentence describing whether your wave would have a high/low pitch, and high/low amplitude.

e. Extra Credit -- Include measurements of your wave in cm (1 square = 0.5 cm

2. Work on other homework quietly.