Light

2. Light • In this unit: • Properties of light • Reflection • Colours • Refraction

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

4. Light travels VERY FAST – around 300,000 kilometres per second or 186,000 km/sec. At this speed it can go around the world 8 times in one second.

5. 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.

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

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

8. 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

9. What happens when light strikes glass? Or waxed paper? Or a book? • If light travels through an object it is =transparent • If light is blocked by an object and a dark shadow is cast it is= opaque. • If some light passes through but not all and a light shadow is present it is=translucent.

10. Transparent objects: • The windows on a school bus, a clear empty glass, a clear window pane, the lenses of some eyeglasses, clear plastic wrap, the glass on a clock, a hand lens, colored glass… • ALL of these are transparent. Yes, we can see through them because light passes through each of them.

11. Opaque objects: • Heavy weight paper, cardboard, aluminum foil, • mirror, bricks, buildings, your eyelids and hands, solid wood door, • All of these objects are opaque because light cannot pass through them at all. • They cast a dark shadow.

12. Translucent objects • Thin tissue paper, waxed paper, tinted car windows, frosted glass, clouds, • All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through.

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

14. 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 !!!

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

16. Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium

19. What is light really?Electromagneticradiationwaves Notice the wavelength is long(Radio waves) and gets shorter (Gamma Rays)

20. *Electromagnetic Radiation • The only difference amongst radio waves, visible light, and gamma-rays is the amount of energy of the photons. Radio waves have photons with low energies. Microwaves have a little more energy than radio waves. Gamma-rays and cosmic rays have highest energy waves and are the deadliest. *Page info from NSTA Conference 2004

21. Diagram and label a representation of a light wave (wavelength, peak, trough)

22. Radio(Longest electromagnetic waves) • Emitted by • Astronomical Objects • Radio Station Transmitters • Detected by • Ground based radio telescopes • *If you turn on a radio,, it will convert the radio wave energy into sound energy.

23. Television • 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.

24. Microwave • Emitted by: • Gas clouds collapsing into stars • Microwave Ovens • Radar Stations • Cell Phones • Detected by • Microwave Telescopes • Food (heated) • Cell phones • Radar (systems)

25. Infrared(Heat or Thermal)Are you a source of infrared? YES you are! • 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

26. VisibleEachcolorisa differentsizewave.Red the longest & violet the shortest

27. UltravioletSunburn / black light He can get skin cancer! • 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)

28. X-ray • Emitted by • Astronomical objects • X-ray machines • CAT scan machines • Older televisions • Radioactive minerals • Airport luggage scanners • Detected by • Space based X-ray detectors • X-ray film • CCD detectors

29. Gamma Ray(Short electromagnetic waves but more energetic) • Emitted by • Radioactive materials • Exploding nuclear weapons • Gamma-ray bursts • Solar flares • Detected by • --Geiger counters • Gamma detectors and astronomical satellites • Medical imaging detectors

30. Sources of g-ray Emission • • Black holes • • Active Galaxies • • Pulsars • • Diffuse emission • • Supernovae • Gamma-ray bursts • • Unidentified

31. COSMIC Rays(The highest energy waves and the deadliest) • Cosmic rays come from deep space and can pass through the Earth.

32. How big are the waves? • A great question! • Radio waves= (Buildings to • human size); • Microwaves • (Humans-beetles); • Infrared waves • (Eye of a needle); • Visible waves • (microscopic size)! • WOW! All the rest are the size of molecules, atoms, atomic nuclei and smaller..

33. Remember radio waves are long…and gamma rays are small Remember radio waves are long…and gamma rays are small Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic

34. Convex Lens • A Convex lens causes light to converge, or focus, producing an image that is smaller than the original object.

35. Concave Lens • A Concave lens causes light to diverge, or spread out, producing a larger image than the original object.

36. eyeglasses flashlights cameras binoculars microscopes Identify some common optical tools, and describe whether each has lenses, mirrors, and/or prisms in it. These should include: Optical Tools

37. Essential Knowledge, Skills, and Processes • Describe the contributions of these scientists in creating and using optical tools: • Galileo Galilei • Robert Hooke • Anton van Leeuwenhoek • Isaac Newton

38. Galileo Galilei • Italian • Lived from 1564-1642 • Developed the refracting telescope • Developed the first known example of the microscope

39. Robert Hooke • English • Lived from 1635-1703 • Devised the compound microscope and illumination system • Discovered plant cells • Examined fossils with a microscope

40. Anton van Leeuwenhoek • Dutch; born in Holland • Lived 1632-1723 • Made over 500 simple microscopes • Discovered bacteria, free-living and parasitic microscopic protists

41. Isaac Newton • English • Lived from 1643-1727 • Discovered that white light was not a simple entity, but splits into a range of colors • When he passed white light through a glass prism, he noted that a spectrum of light was formed; particle theory of light • Reflecting telescope

42. Colour • White light is not a single colour; it is made up of a mixture of the seven colours 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.

43. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet

44. Adding colours • White light can be split up to make separate colours. These colours can be added together again. • The primary colours 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

45. Homework Seeing colour • The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

46. A pair of purple trousers 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 colours: White light

47. Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider a football kit: Shirt looks red White light Shorts look blue

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

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