Waves, Sound, and Light MENU Mechanical Waves Wave PropertiesElectromagnetic Waves Sound Speed of Sound Light Transparent, Translucent, Opaque Color Click above to be taken to that section of the Power Point

Wave Properties

All Waves Crest – very top of wave Trough – very bottom of wave Amplitude – Distance between equilibrium position and crest/trough Wavelength – Distance from the top of one crest to the next crest Frequency – Number of wavelengths to pass by a given point in 1 second. Ex: 2.5 in picture

Frequency vs Wavelength –As frequency increases wavelength decreases –As frequency decreases wavelength increases Wavelength Frequency

Another... Magic !! Remember... –As frequency increases wavelength decreases –As frequency decreases wavelength increases So... Frequency (Hz) = Speed_(m/s)__ Wavelength (m) Measured in Hertz F = 3000 m/s = 10 m

2 Types of Waves MechanicalElectromagnetic 1.Can be transverse 2.Can also be longitudinal (aka compression waves) 1. Always transverse

Mechanical Waves –Mechanical Use matter to transfer energy Examples: water waves, sound waves, energy moving through a slinky.

Mechanical Waves The energy is transferred from particle to particle.

Two Basic Types of Mechanical Waves. Transverse Waves The energy traveling through the wave causes the particles to move at a right angle to the direction of the energy. Example: Ripples on a pond Energy

The Second type of Mechanical Wave Compression Waves (aka Longitudinal Waves) In this type, the particles move in the same direction as the energy. Includes compression and rarefaction (expansion) Example: sound

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Compression Waves (Sound) Frequency and Pitch –As frequency increases, pitch gets higher (soprano) –As frequency decreases, pitch gets lower (tenor) –As amplitude increases, volume gets louder –As amplitude decreases, volume gets softer

Compare sounds: Which is high? Which is low? Which is LOUD ? Which is soft ?

Transverse Wave Examples

Standing Waves Standing wave patterns are produced as the result of the repeated interference of two waves moving in opposite directions in the same medium. All standing wave patterns consist of nodes and antinodes.

Standing Waves Follow one yellow wave – what direction is it going? Now watch a blue wave – what direction is it going? Now, watch the pink wave? How is it different?

Interference What happens when 2 waves collide? Constructive interference – 2 waves add energies 2 small waves = 1 big wave 2 small troughs = 1 deep trough Destructive interference – 2 waves subtract energies 2 equal waves go “flat” 2 unequal waves – one “wins” but is smaller

Sound Sound is a mechanical wave (requires a medium to travel) and a compression wave (molecules colliding) Sound occurs when vibrations transfer energy across molecules as they collide

Sound Sound is produced when an object vibrates. When an object vibrates it exerts a force on the surrounding air Loudness of a sound is recorded in decibels Intensity – amount of energy a sound wave carries per sec through a unit area

Sound The moving air mass carries the sound of the vibration to your ear. “Medium” is what the wave travels through Ex: solid, liquid, gas NO MEDIUM... NO SOUND!! Q. Is there sound in space?

Sound (con’t) Resonance – an increase in amplitude that occurs when external vibrations match another object’s natural frequency –Ex: a singer shatters a crystal glass

The Echo An echo – when a sound wave hits a hard surface and bounces back, causing the sound to be heard a second time Sonar uses echoes. The measure of how long it takes the echo to return to the source of the sound. –Sonar can tell how far away an object is d = v x t d = 343 m/s x 5 s = 1715 m (1.05miles) Speed of sound = 345 m/s in air (Learn to count 5 sec accurately and calculate how far away thunder is!

Sonar vs Ultrasound Sonar – A system of detecting reflected sound waves that at any frequency. –Used by bats and dolphins to find food –Used by humans to “see” things such as airplanes, submarines, unborn babies Ultrasound – Sound waves with frequencies above the normal human range of hearing (frequency too high)

Speed of Sound The speed of sound is different depending on the medium it travels through SlowerFaster Low temp mediumHigh temp medium Less stiff mediumMore stiff medium Low density mediumHigh density medium GasLiquidSolid

Speed of Sound Sound travels at different speeds through different mediums The more dense a material the faster sound travels –345 m/s in air –5,000 m/s in aluminum –3,240 m/s in gold

Speed of Sound Sound travels better through high-density materials –The closer the molecules are together, the faster they can collide and transfer energy

Doppler Effect A perceived upward shift in frequency for observers when the object is going towards them and a perceived downward shift in frequency for observers when the object is going away from them. In other words... it sounds like it has a high pitch coming towards you and a lower pitch after it passes you. Key point – it really never changes!

Both frequency and wavelength are exactly the same for both points A & B so it sounds exactly the same when bug is sitting still. When bug is moving away from Pt A, motion distorts frequencies and it sounds as if it has a higher frequency at Pt B and a lower frequency at Pt A.

Doppler Effect effect-animation/ effect-animation/

Electromagnetic Waves –Electromagnetic Does not need matter to transfer energy Examples: All waves on the electromagnetic spectrum such as radio, TV, microwaves, infrared, visible light, UV, x-rays, & gamma rays

Electromagnetic Waves These waves do not need matter to travel Difference between the different waves is wavelength EM spectrum illustrates the differences Ex: can talk to satellites

Electromagnetic Waves (cont.) Radio – listen to your favorite station Microwaves – call your friends Infrared – night vision Visible light – you can see this presentation Ultraviolet – tanning X-ray – see broken bones Gamma – kill cancerous cells Know these in order!

Light Properties of Light

Light * EM wave that travels transversely (up and down motion) Primary colors are red, green and blue White light is made up of all colors Black is the absence of color

Light (cont.) * We see colors because objects reflect light You see what is being reflected You don’t see what is being absorbed reflects all colors absorbs all colors

Review – What is Light? It is a transverse wave that carries energy It is a small part of the ElectroMagnetic Spectrum Because it is part of the electromagnetic spectrum, it can travel through a vacuum (space)

How do you see the things around you?

Without light, there is no sight!

Light REFLECTS off of objects.

Reflection & Refraction * Reflection is the bouncing back of a wave –Law of Reflection –Law of Reflection – it will reflect back at the same angle as it entered – the “normal” When light enters a new medium at an angle, it causes it to bend toward or away from the “normal” –The “bending” of waves is called refraction Diffraction is the splitting apart of light into its component colors

Refraction

Diffraction – Sound and Light

Which is it?? *

How we see When light strikes an object the light bounces off of the object and then into our eye. For example, the light from the this projector hits the screen and then is reflected to your eye.

Transparent, Translucent, Opaque

Opaque, Translucent, Transparent * opaqueObjects that do not let light pass through them are opaque. Ex. Walls, your desk, the science book translucentObjects that let only some light pass through are translucent. Ex. waxed paper, frosted glass transparentObjects that let light pass clearly through them are transparent. Ex. Windows, plastic wrap, eye glass lenses

Concave & Convex

*

How do glasses work?

Mirror Images in a spoon * Convex MirrorsConcave Mirrors diverge lightconverge light produce smaller, upright image produce larger, upright image if close produce smaller, inverted image if far away

Can light go around corners? Yes, but only with mirrors! Check out the word “TEXT” as it goes around the corners....

Color Red – Green – Blue Cyan-Magenta-Yellow (Ink) (Additive or “all together”) (Subtractive or “nothing”)

COLORS The sun’s light might appear white, but it is a mixture of colors. White light is produced when you mix the colors of the rainbow together.

Light Color Mixing * The primary colors are RED, BLUE and GREEN for light and MAGENTA, YELLOW, and CYAN for computers and paints (pigments).