Presentation on theme: "Electromagnetic waves- transverse waves consisting of changing electric and magnetic fields Carry ENERGY from place to place Different from mechanical."— Presentation transcript:
Electromagnetic waves- transverse waves consisting of changing electric and magnetic fields Carry ENERGY from place to place Different from mechanical waves…how?
An electric field exerts forces on charged particles Electric fields are produced by charged particles changing magnetic fields A magnetic field produces magnetic forces Magnetic fields are produced by magnets changing electric fields vibrating charges
As the two fields regenerate each other, their E travels in the form of a wave. EM waves DONT need a medium!!! Can travel through a vacuum (=empty space) OR through matter EM radiation – the transfer of E by EM waves traveling through matter or across space.
What is faster…speed of sound or light? Light travels much faster than sound. For example: What is faster…speed of sound or light? 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.
First accurate estimations were in 1926 when Albert Michelson completed his experiment in California.
Light (and all EM waves) travel the same speed in a vacuum… c = 3.00 x 10 8 m/s Or 300,000,000 m/s (compared to ~ 340 m/s) Thats 8 times around the earth in 1 second!!!!
EM waves vary in and frequency c = * frequency Since the speed of light (c) is always 3.00 x 10 8 m/s, you can always calculate from frequency and vice versa.
EM radiation sometimes behaves like a wave, and sometimes like a stream of particles. There is evidence for both theories... Thats called wave-particle duality In some experiments, the wave model works best. In other experiments, the particle model works best. Thus, we use both
Light Photons ElectromagneticRadiation
Double Slit Experiment Pass light through two slits and an interference pattern is observed Interference is a property of waves!
Photoelectric Effect Light shown on a metal can cause electrons to be emitted from the metal Photons- particles of light The greater the frequency of an EM wave, the more E each of its photons has
Intensity- the rate at which a waves energy flows through a given unit of area…basically, it is brightness of light. As you leave the source of light, does intensity increase or decrease?
Farther from the source, the photons spread out over a larger area, and intensity decreases.
What happens when you put a prism in front of a window?
EM spectrum- the full range of frequencies of EM radiation How many different types of EM waves can you think of? EM Spectrum includes: Radio waves Infrared rays Visible light UV rays X-rays Gamma Rays
Shorter than radio, also used to carry messages (pictures & sound) to our TV sets. We can sense the TV waves around us with our televisions.
Emitted by: Gas clouds collapsing into stars Microwave Ovens Radar Stations Cell Phones Detected by Microwave Telescopes Food (heated) Cell phones Radar (systems)
Emitted by Sun and stars (Near) TV Remote Controls Food Warming Lights (Thermal) *Everything at room temperature or above,=HEAT Detected by Infrared Cameras TVs, VCRs, Your skin
Emitted by The sun and other astronomical objects Laser pointers Light bulbs Detected by Cameras Human eyes Plants (red light) Telescopes
Emitted by Tanning booths (A) The sun (A) Black light bulbs (B) UV lamps Detected by Space based UV detectors UV Cameras Flying insects (flies)
Emitted by Astronomical objects X-ray machines CAT scan machines Radioactive minerals Airport luggage scanners Detected by Space based X-ray detectors X-ray film
Emitted by Radioactive materials Exploding nuclear weapons Solar flares Detected by Geiger counters Gamma detectors and astronomical satellites Medical imaging detectors
Cosmic rays come from deep space and can pass through the Earth.
When you are looking at things, anything, what you are really seeing is light. We cant see through walls because light doesnt pass through walls.
We see things because they reflect light into our eyes: Homework
How light behaves when it strikes an object depends on many factors, including the material the object is made of Materials can be translucent, transparent, or opaque.
Transparent objects- No scattering Color transmitted is color you see and all other colors are absorbed Translucent- Light is scattered and transmitted some Opaque- Light is either totally reflected or absorbed Color of opaque objects is color it reflects
When light strikes a new medium, the light can be reflected, absorbed, or transmitted. When light is transmitted, it can be refracted, polarized, or scattered.
Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror
The Law of Reflection Angle of incidence = Angle of reflection The same !!!
Smooth, shiny surfaces have a specular reflection: Rough, dull surfaces have a diffuse reflection Diffuse reflection is when light is scattered in different directions
Two examples: 1) A periscope 2) A car headlight
The bending of light waves as they pass from one medium to another Results in mirages, which are false or distorted images
Inferior Mirages: formed when the air near the ground is very warm compared to the air just above it.
Polarized light is light that all vibrate in the same plane (or direction!)
Light is redirected as it passes through a medium. This is responsible for our red sunsets!
White light- 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.
Red Orange Yellow Green Blue Indigo Violet
Adding Colors White light can be split up to make separate colors. These colours can be added together again The 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 all three makes white again Adding red and green makes yellow
Seeing Color The color an object appears depends on the colors of light it reflects For example, a red book only reflects red light: White light Only red light is reflected
A 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 light White light
Color Blind Tests
If 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)
LIGHT & ITS USES: Lenses Convex lenses Thicker in the center than edges. Lens that converges (brings together) light rays. Forms real images and virtual images depending on position of the object The images formed are upside down
Vision The eye is a convex lens Retina Lens refracts light to converge on the retina and then nerves transmit the image Rods Nerve cells in the retina. Very sensitive to light & dark Cones Nerve cells help to see light/color
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.
How You See Near Sighted – Eyeball is too long and image focuses in front of the retina Far Sighted – Eyeball is too short so image is focused behind the retina.
LIGHT & USES: Optical Instruments LASERS Holography – Use of Lasers to create 3-D images Fiber Optics – Light energy transferred through long, flexible fibers of glass/plastic Uses – Communications, medicine, t.v. transmission, data processing.