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Light

Light. Properties of light Reflection Colors Refraction. LIGHT: What Is It?. Light Energy Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level.

phailin-suttikul
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Light

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  1. Light • Properties of light • Reflection • Colors • Refraction

  2. LIGHT: What Is It? • Light Energy • Atoms • As atoms absorb energy, electrons jump out to a higher energy level. • Electrons release light when falling down to the lower energy level. • Photons - bundles/packets of energy released when the electrons fall. • Light: Stream of Photons

  3. Moving photon creates electric & magnetic field • Light has BOTH Electric & Magnetic fields at right angles! • Energy is perpendicular to direction of motion Transverse Waves

  4. Electromagnetic Spectrum

  5. Electromagnetic Spectrum • Invisible Spectrum • Radio Waves • Infrared Rays • Ultraviolet rays • X-Rays • Gamma rays

  6. Visible Spectrum – Light we can see • Largest to Smallest Wavelength. • Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet. Don’t forget those sexy birds…

  7. Laser Part 1 – Properties of Light • Light travels in straight lines:

  8. Light travels VERY FAST – around 300,000 kilometres per second. • C = 3.0 x 108 m/s At this speed it can go around the world 8 times in one second. Speed of light = frequency x wavelength C = f λ

  9. What is the wavelength range for the FM radio band (88 MHz-108 MHz)? • C = f λ C/f = λ • 3.0 x 108 m/s / 88 x 106 = 3.4 m • 3.0 x 108 m/s / 108 x 106 = 2.78 m • The portion of the visible spectrum appears brightest to humans around 560 nm in wavelength. What is the frequency of 560 nm light? • C = f λ C/λ = f • 3.0 x 108 m/s / 560 x 10-9 = • 5.4 x 1014 Hz

  10. Thunder and lightning start at the same time, but we will see the lightning first. • Light travels much faster than sound. For example: • 2) When a starting pistol is fired we see the smoke first and then hear the bang.

  11. We see things because they reflect light into our eyes: Homework

  12. Rays of light Shadows are places where light is “blocked”: • Shadows

  13. Brightness • Brightness decreases by the square of the distance from the source. • THE FURTHER YOU ARE FROM THE LIGHT THE LESS BRIGHT IT IS • If you move twice as far away from the light source, ¼ as much light falls

  14. Properties of Light summary • Light travels in straight lines • Light travels much faster than sound • We see things because they reflect light into our eyes • Shadows are formed when light is blocked by an object • Brightness affected by distance

  15. Reflection • DEFINITION: the turning back of an electromagnetic wave at the surface of a substance • Most substances absorb some light and reflect the rest. (no surface is a perfect reflector)

  16. Specular vs. Diffuse Reflection • Smooth, shiny surfaces have a specular reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

  17. Using mirrors • Two examples: 2) A car headlight 1) A periscope

  18. Part 2 - Reflection Normal • Reflection from a mirror: Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

  19. Angle of incidence = Angle of reflection • The Law of Reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

  20. Flat Mirrors • Object distance (p): the distance the object is from the mirror • Image distance (q): the distance the image appears to be behind the mirror’s surface • The object and image distances are equal. The image and the object are the same size.

  21. Virtual image • A flat mirror always forms a virtual image. • You can only see this behind the mirror • Cannot be displayed on a physical surface

  22. 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.

  23. The colors of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet

  24. 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 blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

  25. Homework 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

  26. A pair of purple britches 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

  27. Using colored light • If we look at a colored object in colored light we see something different. For example, consider a soccer jersey: Shirt looks red White light Shorts look blue

  28. Red light Shirt looks red • In different colors of light this kit would look different: Shorts look black Shirt looks black Blue light Shorts look blue

  29. Homework Some further examples:

  30. Red Filter Magenta Filter Using filters • Filters can be used to “block” out different colors of light:

  31. Investigating filters

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