# Waves Sound Waves and Electromagnetic Waves Georgia Performance

• Slides: 29

Waves Sound Waves and Electromagnetic Waves

Georgia Performance Standards SPS 9. 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 Wave y-axis IN A MECHANICAL WAVE, Amplitude shows how much energy a wave has. x-axis If a sound wave has very little amplitude, the sound would be Like a whisper or soft.

Parts of a wave Wavelength is measured from crest to crest or or trough to trough 1 wave= A complete crest and a complete trough Wavelength is measured in meters. The crest is the highest point of a wave. The trough is the Lowest point of wave.

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. 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 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 waves 2. Ocean waves 3. Wave on a rope transverse compressional Examples of Compressional Waves: 1. Sound waves

Transverse or Compressional? Label, Wavelength, Amplitude, Crest and Trough _______ rarefactions compression ________

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 cancelling headphones

Wave Behaviors 1. Reflection: when a wave strikes an object and bounces back. • Examples: Mirror Image and Echoes Reverberation below… bouncing Off 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 Interactions 2. 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 • In • • • Higher frequency: In E-waves: higher freq, higher energy In Sound waves: higher freq, higher pitch 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)

Doppler Effect Doppler Shift

Speed of sound In air…. 347 m/s In water… 1498 /s In aluminum… 4877 m/s Terms Intensity--- amount of energy that flows through a certain area at a certain time Loudness– human perception of sound intensity Decibels– units to measure sound intensity or loudness • Above 120 d. B 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/ai rspace/doppler/en/doppler_exp. htm? width=750&height =460&popup=true http: //science. howstuffworks. com/dictionary/physicsterms/doppler-effect-info. htm Doppler Shift: http: //zebu. uoregon. edu/~soper/Light/doppler. html Seeing Color: (Read and Watch Powerpoint) http: //askabiologist. asu. edu/biology-bits/seeing-colorbits