Waves

Sound Waves and Electromagnetic Waves

Georgia Performance Standards

SPS9. Students will investigate the properties of waves.

a. Recognize that all waves transfer energy.

b. Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves.

c. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves.

d. Investigate the phenomena of reflection, refraction, interference, and diffraction.

e. Relate the speed of sound to different mediums.

f. Explain the Doppler Effect in terms of everyday interactions.

What is a wave?

• A rhythmic disturbance that transfers energy through matter or space.

• The wave exists only as long as it has energy to carry

When a wave hits a boat, does it carry the boat along? Explain. NO, the matter (water) moves up and down, the wave moves horizontally.

What is the source of a wave?

• Vibrations cause waves.

• Vibrations are REPEATING DISTURBANCES.

• When an object vibrates, it is moving, therefore it has energy which is given off to a nearby particle causing them to vibrate as well.

Mechanical Waves• Some waves must have substance to travel

through and some do not.

Mechanical Waves must have a material to travel through (vibrate the particles).

• Sound waves, ocean waves, waves on a rope are mechanical waves.

• The material that waves travel through is called the medium.

Mediums:• Sound waves travel through solids, liquids or gas.• Ocean waves travel through water.

Parts of a WaveIN A MECHANICAL WAVE,Amplitude shows how much energy a wave has.

If a sound wave has very little amplitude, the sound would be

Like a whisper or soft.

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Parts of a waveWavelength is measured from crest to crest or

or trough to trough

Wavelength is measured in meters.

The crest is the highest point of a wave. The trough is the Lowest point of wave.

1 wave=A complete crestand a complete trough

Frequency of Waves• Frequency is the number of waves that

cross a point in a given amount of time.

• Measured in Hertz• 1 Hertz = 1 wave/sec A.

B.

Which has a higher frequency?A or B? a

Which has a higher amplitude?A or B? they are the same

Which has a greater wavelength?A or B? B

Calculate frequency

1 wave consists of 1 crest + 1 trough freq= # waves/ time it takes to pass a point

6 seconds here

Frequency = 3.5 waves/ 6 sec = .58 Hz

Types of Waves

1. Transverse Waves: waves where the matter in the medium moves back and forth at right angles to the direction that the wave travels

• Has crests and troughs

2. Compressional Waves: a type of wave where the matter in the medium moves back and forth in the same direction that the wave travels.

• Has compressions and rarefactions• Also called Longitudinal waves

Compression Wave

What is a rarefaction? Molecules spread out in a compression wave

What is a compression? Molecules compressed (squished together) in compression wave

Transverse Waves vs Compressional Waves

Examples of Transverse waves:1. Electromagnetic waves2. Ocean waves3. Wave on a rope

Examples of Compressional Waves:1. Sound waves

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compressional

Transverse or Compressional?

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Label,Wavelength,Amplitude, Crest andTrough

______________

_______________

INTERFERENCE

• Interference occurs when two (or more) waves are traveling through the same medium at the same time and interact.

Constructive Interference• When two waves combine to form in a way

that it produces a larger wave.

• Crest of one wave meets crest of another wave (or trough meets trough)

Larger wave

Destructive Interference• When two waves interact in a way that forms a

smaller wave.• When the crest of one wave meets the trough of

another wave

Example: Noise cancellingheadphones

Wave Behaviors

1. Reflection: when a wave strikes an object and bounces back.

• Examples: Mirror Image and Echoes

Reverberation below… bouncingOff walls and getting louder…(reflected sound wave)

Reflection of Waves

Echolocation….(Reflected sound)

SONAR… Sound Navigation and Ranging

(reflected sound wave)RADAR…. RAdio Detection And Range

(reflected Ewave)Seeing Colors (reflected Ewaves)

Wave Interactions2. Refraction: the bending of a wave caused by a change in speed due to a change in medium.• Examples: pencil looks bent in water, rainbow

Interaction of Waves

3. Diffraction: occurs when an object causes a wave to change direction and bends around it.

Light

Sound

Electromagnetic Waves• Created by vibrating electric charges• Can travel through a vacuum (needs NO medium to travel

through)• Have a wide variety of frequencies and wavelengths.• People can only see the wavelengths around 400 nanometers to 700 nanometers.• All travel at the speed of

light in a vacuum– 300,000 km/s – 670, 617, 000 mi/hr

Electromagnetic Spectrum• A device for organizing the

electromagnetic waves by frequency and wavelength.

Frequency and Waves• Higher frequency:

In E-waves: higher freq, higher energyIn Sound waves: higher freq, higher

pitchIn sound waves….• Humans can only hear sound waves

between 20 Hz and 20,000 Hz• Ultrasonic– above 20,000 Hz

bats, whales, dolphins, cats, dogs, ultrasound• Infrasonic– below 20 Hz

elephants

Doppler Effect• Change in pitch or frequency that occurs

when the source of a sound wave is moving relative to an observer.

Lower pitch sound Higher pitch sound(higher freq of waves)

ambulance.au

Doppler Effect

Doppler Shift

Speed of soundIn air…. 347 m/sIn water… 1498 /sIn aluminum… 4877 m/s

Terms

Intensity--- amount of energy that flows through a certain area at a certain time

Loudness– human perception of sound intensityDecibels– units to measure sound intensity or loudness

•Above 120 dB can cause pain in ears

Speed of Waves in different mediums

What happens to the speed of sound as it moves from a solid to liquid to gas?

Why? Slows down cause particles get farther apart and particles take longer to bump into each other and pass on energy.

What happens to the speed of light (ewaves) as it move from a solid to a liquid to a gas?

Why? Speeds up, ewaves don’t need a medium, particles just slow them down. They move fastest through a vacuum…. No medium.

Speed of Sound in different temperatures

What happens to the speed of sound as the temperature increases in a material?

Why? As temperature increases, speed of sound increases. Particles move faster and bump into each other more.

True or False?Sound waves move faster through cold air than hot air. _____Sound waves move faster through water than air. _________Radio waves move faster through air than a vacuum._______Sound waves move faster through a vacuum than air. _______

Gamma rays move faster than light waves through air. ______

Go to these websites and TAKE NOTES…

Doppler Effect:http://www.planetseed.com/files/flash/science/lab/airspace/doppler/en/doppler_exp.htm?width=750&height=460&popup=true

http://science.howstuffworks.com/dictionary/physics-terms/doppler-effect-info.htmDoppler Shift:http://zebu.uoregon.edu/~soper/Light/doppler.htmlSeeing Color: (Read and Watch Powerpoint)http://askabiologist.asu.edu/biology-bits/seeing-color-bits