2Electromagnetic Waves Electromagnetic waves- transverse waves consisting of changing electric and magnetic fieldsCarry ENERGY from place to placeDifferent from mechanical waves…how?
3How are EM Waves produced? An electric field exerts forces on charged particlesElectric fields are produced bycharged particleschanging magnetic fieldsA magnetic field produces magnetic forcesMagnetic fields are produced bymagnetschanging electric fieldsvibrating charges
4How do EM waves travel?As the two fields regenerate each other, their E travels in the form of a wave.EM waves DON’T need a medium!!!Can travel through a vacuum (=empty space) OR through matterEM radiation – the transfer of E by EM waves traveling through matter or across space.
5What is faster…speed of sound or light? Light travels much faster than sound. For example: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.
6Speed of LightFirst accurate estimations were in 1926 when Albert Michelson completed his experiment in California.
7Speed of Light c = 3.00 x 108 m/s Or 300,000,000 m/s Light (and all EM waves) travel the same speed in a vacuum…c = 3.00 x 108 m/sOr 300,000,000 m/s(compared to ~ 340 m/s)That’s 8 times around the earth in 1 second!!!!
8l and frequency EM waves vary in l and frequency c = l * frequency Since the speed of light (c) is always x 108 m/s, you can always calculate l from frequency and vice versa.
9Wave or Particle???EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.There is evidence for both theories...That’s called wave-particle dualityIn some experiments, the wave model works best.In other experiments, the particle model works best.Thus, we use both
13Particle… Photons- particles of light Photoelectric EffectLight shown on a metal can cause electrons to be emitted from the metalPhotons- particles of lightThe greater the frequency of an EM wave, the more E each of its photons has
18The Waves of the Spectrum What happens when you put a prism in front of a window?
19The EM SpectrumEM spectrum- the full range of frequencies of EM radiationHow many different types of EM waves can you think of?EM Spectrum includes:Radio wavesInfrared raysVisible lightUV raysX-raysGamma Rays
22TelevisionShorter than radio, also used to carry messages (pictures & sound) to our TV sets.We can sense the TV waves around us with our televisions.
23Microwave Emitted by: Detected by Gas clouds collapsing into stars Microwave OvensRadar StationsCell PhonesDetected byMicrowave TelescopesFood (heated)Cell phonesRadar (systems)
24Infrared (Heat or Thermal) Are you a source of infrared? YES you are! Emitted bySun and stars (Near)TV Remote ControlsFood Warming Lights (Thermal)*Everything at room temperature or above,=HEATDetected byInfrared CamerasTVs, VCRs,Your skin
25Visible Each color is a different size wave Visible Each color is a different size wave. Red the longest & violet the shortestEmitted byThe sun and other astronomical objectsLaser pointersLight bulbsDetected byCamerasHuman eyesPlants (red light)TelescopesRoyG.Biv
26Ultraviolet Sunburn / black light He can get skin cancer!Emitted byTanning booths (A)The sun (A)Black light bulbs (B)UV lampsDetected bySpace based UV detectorsUV CamerasFlying insects (flies)
27X-ray Emitted by Detected by Astronomical objects X-ray machines CAT scan machinesRadioactive mineralsAirport luggage scannersDetected bySpace based X-ray detectorsX-ray film
28Gamma Ray (Short electromagnetic waves but more energetic) Emitted byRadioactive materialsExploding nuclear weaponsSolar flaresDetected by Geiger countersGamma detectors and astronomical satellitesMedical imaging detectors
29COSMIC Rays (The highest energy waves and the deadliest) Cosmic rays come from deep space and can pass through the Earth.
31Light and MaterialsWhen you are looking at things, anything, what you are really seeing is light.We can’t see through walls because light doesn’t pass through walls.
32We see things because they reflect light into our eyes: Homework
33Light and Materials, ctd. How light behaves when it strikes an object depends on many factors, including the material the object is made ofMaterials can be translucent, transparent, or opaque.
34Transparent objects- Translucent- Opaque- No scattering Color transmitted is color you see and all other colors are absorbedTranslucent-Light is scattered and transmitted someOpaque-Light is either totally reflected or absorbedColor of opaque objects is color it reflects
35Interactions of LightWhen light strikes a new medium, the light can be reflected, absorbed, or transmitted.When light is transmitted, it can be refracted, polarized, or scattered.
36Reflection Mirror Reflection from a mirror: Normal Angle of incidence Incident rayReflected rayAngle of incidenceAngle of reflectionMirror
37Angle of incidence = Angle of reflection The Law of ReflectionAngle of incidence = Angle of reflectionThe same !!!
38Clear vs. Diffuse Reflection Smooth, shiny surfaces have a specular reflection:Rough, dull surfaces have a diffuse reflectionDiffuse reflection is when light is scattered in different directions
39Using mirrorsTwo examples:2) A car headlight1) A periscope
40RefractionThe bending of light waves as they pass from one medium to anotherResults in mirages, which are false or distorted images
41Inferior Mirages:formed when the air near the ground is very warm compared to the air just above it.
42PolarizedPolarized light is light that all vibrate in the same plane (or direction!)
43Scattering Light is redirected as it passes through a medium. This is responsible for our red sunsets!
45We can demonstrate this by splitting white light with a prism White light- not a single color; it is made up of a mixture of the seven colors of the rainbowWe can demonstrate this by splitting white light with a prismThis is how rainbows are formed: sunlight is “split up” by raindrops.
47Adding ColorsWhite light can be split up to make separate colors. These colours can be added together againThe primary colors of light are red, blue and green:Adding blue and red makes magenta (purple)Adding blue and green makes cyan (light blue)Adding red and green makes yellowAdding all three makes white again
48Only red light is reflected Seeing ColorThe color an object appears depends on the colors of light it reflectsFor example, a red book only reflects red light:HomeworkWhite lightOnly red light is reflected
49A white hat would reflect all seven colors: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):Purple lightA white hat would reflect all seven colors:Whitelight
66Do you see gray areas in between the squares Do you see gray areas in between the squares? Now where did they come from?
67If you continue to focus on the sign in the centre of the image you will notice that the circle of violet circles will soon disappear completely, and you will see only the green spot (which is actually violet)
68LIGHT & ITS USES: Lenses Convex lensesThicker in the center than edges.Lens that converges (brings together) light rays.Forms real images and virtual images depending on position of the objectThe images formed are upside down
72Vision Retina Rods Cones The eye is a convex lens Lens refracts light to converge on the retina and then nerves transmit the imageRodsNerve cells in the retina. Very sensitive to light & darkConesNerve cells help to see light/color
73PARTS OF EYE CONTINUED… Rods – responsible for black and white vision and detection of motion.Cones – Seeing in color and visual acuity. We have three types of cones: cones that see red, cones that see blue, and cones that see green.
74How You SeeNear Sighted – Eyeball is too long and image focuses in front of the retinaFar Sighted – Eyeball is too short so image is focused behind the retina.
75LIGHT & USES: Optical Instruments LASERSHolography – Use of Lasers to create 3-D imagesFiber Optics – Light energy transferred through long, flexible fibers of glass/plasticUses – Communications, medicine, t.v. transmission, data processing.