Waves • A disturbance that transfers energy from place to place. • Energy = the ability to do work. • Created when a source of energy causes a medium to vibrate
Mechanical Waves • Waves that require a medium to travel through. • Medium = material a wave travels through • Note: Electromagnetic waves (like light) do not require a medium. So they are not mechanical waves.
Wave Terms Frequency- the number of complete waves that pass a given point in a certain amount of time. Amplitude-the maximum distance the particles of a medium move away from their rest position as a wave passes through the medium. Pitch-perception of the frequency of a sound Wave-A disturbance that transfers energy from place to place. Medium- Substance a wave travels through
Drawing sounds… This sound wave has a _____ frequency: This sound wave has a ___ _frequency:
Drawing sounds… This sound wave has a _____ amplitude (loud): This sound wave has a _____ amplitude (quiet):
Light and Sound In this unit: 1) 2) 3) 4) 5) 6) Properties of sound Hearing Properties of light Reflection Colors Refraction
Sound • Begins with a vibration • Travels longitudinally through a medium (solid, liquid or gas) • Humans make sound by vibrating vocal cords found in the larynx. • Due to diffraction sound can bend around corners.
Sound – The basics We hear things when they vibrate. If something vibrates with a high frequency (vibrates very ______) we say it has a _____ pitch. If something vibrates with a low frequency (vibrates ______) we say it has a ____ pitch. The lowest frequency I could hear was… Words – slowly, low, high, quickly
Resonance • Most objects naturally vibrate. • When a wave passes through a material at the same frequency as the natural vibration. • Can cause the natural object to start vibrating more strongly.
You Tube video http: //www. youtube. com/watch? v=IZD 8 ff. Pw XRo&feature=rec-LGOUT-real_rn-HM
Other sound effects… Like light, sound can be… 1) Reflected – sound reflections are called ______. 2) Refracted – this is why you might sound strange if you try talking underwater
Interference • • • Interference When two or more waves meet. They will have an effect on one another. Constructive Interference – Waves combine and make a new wave with larger amplitudes. – If wavelengths are the same the crests will be at the same point. The crests will be added together to make a larger amplitude. Destructive Interference – Waves combine and make smaller amplitudes. – If crests don’t meet at the same place they cancel each other out making smaller amplitudes. – If the crest lines up with the trough the waves will cancel exactly. This produces amplitudes of zero. Standing Waves – A wave that appears to stay in one place. – Is interference as two waves pass each other in opposite directions. – Nodes = areas of zero amplitude. – Antinodes = areas of crests and troughs
Properties of Sound • • Intensity – The amount of energy the wave carries per second through a unit area. – Measured in watts per square meter (W/m 2) – Larger the amplitude the higher the intensity. Loudness – Describes what you hear. – Measured in decibels (d. B). – A sound wave of greater intensity is heard as a louder sound. Frequency – The number of vibrations that happen per second. – Frequency range of human hearing = 20 Hz – 20, 000 Hz. • Above 20, 000 Hz = ultrasound • Below 20 Hz = infrasound Pitch – Describes what you hear (high or low). – High frequency = high pitch. – Low frequency = low pitch.
Speed of Sound • Depends on the properties of the medium it travels through. • Medium properties = elasticity, density, and temperature. – Elasticity • Is the ability of a material to bounce back after being disturbed (stretched rubber band vs. ’ stretched clay) • Sound moves faster through mediums that have high elasticity • Solids usually more elastic than liquids or gases. • Gases less elastic than liquids. – Density • Is the amount of matter or mass there is in a given space or volume. • Sound moves slower in denser materials like lead, iron or steel. – Temperature • Sound moves slower at lower temperature
Doppler Effect • The apparent change in frequency as a wave source changes position relative to the listener. • Move towards listener = higher pitch. – Waves reach listener with a higher frequency. • Move away from listener = lower pitch. – Waves reach listener with a lower frequency.
Types of Mechanical Waves • Three types based on the way the wave moves. • Transverse – Medium moves at right angles to the direction of wave movement – Top = crest; Bottom = trough; middle = rest position – Ex: Rope Wave • Longitudinal – Medium and wave move in same direction. – Area close together = compression; Area spread out = rarefaction – Ex: Springs • Surface waves – Combination of transverse and longitudinal – Occurs at surface between two mediums like water and air. – Works in a circle.
Wave Interactions • • Wave Interactions Reflection – The bouncing back of a wave when hitting a substance it can not penetrate. – Angle of incidence (degree of angle wave hits barrier at) = Angle of reflection (degree of angle wave bounces off at). Refraction – Bending of a wave due to change in speed. – Wave enters a new medium at an angle and the new medium causes a change in speed causing the wave to bend. Diffraction – Bending of waves around the edge of barriers. – Waves bend and spread out as they pass barriers or holes in barriers.
Wave Properties • • • Basic properties are amplitude, wavelength, frequency and speed. Amplitude – A direct measure of the wave’s energy. – Larger amplitude = more energy. – Transverse = distance from rest position to crest or rest position to trough. • Lager distance = higher amplitude. – Longitudinal = how crowded the compressions or how spread out the rarefactions. • More crowded compressions and spread rarefaction = higher amplitude. Wavelength – Distance between two corresponding parts of a wave. – Transverse = distance from crest to crest or trough to trough. – Longitudinal = distance form compression to compression. Frequency – Number of complete waves that pass a given point in a certain amount of time. – Number of vibrations per second. – Measured in unit called Hertz (Hz). Speed – Different waves travel at different speeds. – Speed = (Wavelength) (Frequency) – Given the same conditions the same type of wave will have the same speed.
Hearing • • Outer ear funnels sound to the middle ear → middle ear transmits the sound to the inner ear → inner ear converts the sound to a form the brain understands. Outer Ear – The ear looks like a funnel and moves the sound wave to the ear canal and ultimately to the ear drum. The ear drum vibrates. Middle Ear – Contains three bones (hammer, anvil and stirrup). – Hammer picks up the vibrations of the ear drum and transmits them through the anvil which shakes the stirrup. Inner Ear – Shaking stirrup transmits the energy through a membrane to the liquid filled cochlea. The energy in the liquid moves tiny hairs attached to nerve cells which transmit the sound to the brain.
Hearing problems Our hearing range can be damaged by several things: 1) Too much ear wax! 2) Damage to the auditory nerve 3) Illness or infections 4) Old age (not like Mr Donath)
The Ear Label your diagram with the following: 1 These bones are vibrated by the eardrum 2 This tube carries the sound towards the eardrum 3 This part is used to help us keep our balance 4 This part “picks up” the vibrations 5 This part of the ear contains many small hairs with turn vibrations into an electrical signal 6 This part connects the ear to the mouth 7 This part “channels” the sound towards the ear drum
Part 1 – Properties of Light travels in straight lines: Laser
Light travels VERY FAST – around 300, 000 kilometers per second. At this speed it can go around the world 8 times in one second.
Electromagnetic Waves • Transverse waves with electrical and magnetic properties that do not require a medium. • Electromagnetic radiation = energy transferred by wave. • Speed in a vacuum = 300, 000 meters per second. • All travel at the same speed. – Speed = Wavelength x Frequency – So as wavelength decreases the frequency must increase. • Can be used in many applications – Microwaves, radar, MRI, thermograms, and X-rays.
Light travels much faster than sound. For example: 1) Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.
Light hitting an object • • • Light can be reflected = bounced back; Absorbed = no light passes; or Transmitted = passes right through Materials Opaque – Reflects or absorbs all light – Can not see through them – Ex: wood, metal, cotton Transparent – Transmits light – Can see through them – Ex: clear glass, water, air Translucent – Scatters light as it passes; some light passes – Can tell something is on the other side but you can’t make out details – Ex: frosted glass, wax paper
Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Reflectors
We see things because they reflect light into our eyes: Homework
Shadows are places where light is “blocked”: Rays of light
Properties of Light summary 1) Light travels in straight lines 2) Light travels much faster than sound 3) We see things because they reflect light into our eyes 4) Shadows are formed when light is blocked by an object
Part 2 - Reflection from a mirror: Normal Reflected ray Incident ray Angle of incidence Angle of reflection Mirror
The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at _____ angle it hits it. The same !!!
Kinds of Reflection • You see most objects because light reflects (bounces) off them. • Law of Reflection – Rays = straight lines that represent the light waves – Angle of Incidence = Angle of Reflection • Angle of Incidence = angle light hits surface • Angle of reflection = angle light bounces off surface • Regular Reflection – Occurs on smooth surface – Parallel incidence rays all reflect at the same angle • Diffuse Reflection – Occurs on a uneven surface (bumpy)
Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions
Using mirrors Two examples: 2) A car headlight 1) A periscope
Mirrors • Produce an image or copy of an object formed by reflected or refracted light. • Can be flat or curved • Plane Mirror – Is a flat mirror – Image is right-side up and the same size as the object – Produces a virtual image = appears to come from behind the mirror • Concave Mirror (Con. CAVE) – Is an inwardly curved mirror (like the inside of a bowl, or like a cave). – Reflects parallel rays so they meet at a point = focal point – Can form virtual or real images depending on the position of the object. • Convex Mirror – Is an outwardly curved mirror – Spread out rays that appear to come from a focal point behind the mirror
Light Refraction • Bending of light when it enters a new medium due to change in speed • Prisms – Each wavelength of light is refracted at a different angle revealing all the colors of the rainbow. • Rainbow – Raindrops act like tiny prisms revealing the colors of the rainbow • Mirages – Image of distant object caused by refraction of light.
Refraction is when waves ____ __ or slow down due to travelling in a different _____. A medium is something that waves will travel through. When a ruler is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the ruler to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium
Lenses • Curved pieces of glass or other materials that refract light • Concave Lenses – Thinner in the center – Produce virtual images because rays are spread out as they pass • Convex Lenses – Thicker in center – Type of image depends on position of object. – Farther away than focal point = real image past the lens – Closer than focal point = virtual image on same side of lens
Color • Color you see is the wavelength of color the object reflects. • Primary Colors – Three colors used to make every other color. – Red, Green, Blue • Secondary Colors – Two primary colors mixed in equal amount. • White light (all colors mixed)
Color White light is not a single color; it is made up of a mixture of the seven colors of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.
The colors of the rainbow: Red Orange Yellow Green Blue Indigo Violet
Adding colors White light can be split up to make separate colors. These colors can be added together again. The primary colors of light are red, blue and green: Adding blue and red makes magenta (purple) Adding red and green makes (yellow) Adding blue and green makes (light blue) Adding all three makes white again
Seeing color The color of an object depends on the color of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected
A pair of purple pants would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colors: White light
Using colored light If we look at a colored object in colored light we see something different. For example, consider the pants and shirt: Shirt looks red White light Shorts look blue
In different colors of light this outfit would look different: Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue
Some further examples: Object Red socks Blue teddy Color of light Color object seems to be Red Blue Black Green Black Red Black Blue Green Red Green camel Blue Green Red Magenta book Blue Green
Using filters Filters can be used to “block” out different colors of light: Red Filter Magenta Filter
Investigating filters Color of filter Red Green Blue Light blue Magenta Yellow Colors that could be “seen”
Red Yellow Blue Green Magenta White
Eye • • Organ that lets you see light. Cornea – Transparent front surface – Allows light to enter the eye Iris – muscle that adjusts the amount of light entering the eye – gives the eye color Pupil – Opening to eye (controlled by iris) – Wide in low light; smaller in bright light Lens – Convex lens that focuses light on the retina Retina – contains light sensitive rods and cones that generate a nerve signal – Rods distinguish black and white – Cones distinguish color Optic Nerve and Brain – optic nerve takes signal from rods and cones and wends it to the brain where it is interpreted.