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Unit 3 – Part 1 The History of Light

Unit 3 – Part 1 The History of Light. The Challenge of Light. We have been studying light for years Do we know everything about it? Absolutely not! Greeks & Chinese had been using light for years with no real concept of how to use it or how it worked … do you want proof? Archimedes!.

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Unit 3 – Part 1 The History of Light

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  1. Unit 3 – Part 1 The History of Light

  2. The Challenge of Light • We have been studying light for years • Do we know everything about it? • Absolutely not! • Greeks & Chinese had been using light for years with no real concept of how to use it or how it worked … do you want proof? Archimedes!

  3. Archimedesborn 287 BC • A Greek scientist • Believed you could uselight from the sun and, using a lot mirrors,reflect that light to … • Burn enemy ships Do you think it worked?

  4. Archimedes • Absolutely, 100%, not even one bit … at all! • He had the idea of a laser beam before star wars. • Why do you think it did not work? MythBusters

  5. The Early Years • Many people want to study and understand light • One of the 1st theorists was Pythagoras(born 570 BC) • His theory … • Light was made of beams • Beams came out of a person’s eyes in straight lines • Sight occurred when these beams touched an object

  6. The Early Years

  7. The Early Years • What is the major flaw we can see with this theory? • If that is how light worked … we would all be able to see in the dark! • Who else guessed? • Euclid (born ~300BC) • He discovered when light hits a flat mirror that the reflected light is the same angle coming off

  8. Fast Forward To 1000AD • Meet Ibn Al-Haytham • Born in Basra,Iraq….Moved To Egypt. • The Father of Science • What did he do?

  9. What Did Ibn Al-Haytham Do? • Ibn Al Haytham invented the rules of proper scientific testing (controlled variables, 1 manipulated variable, etc) • Every single scientific test run today follow his carefully designed system. • Wrote the greatest science textbook of all time while imprisoned in his house for 10 years. • The name of the book is “Kitab al Manazir” (The book of Optics)

  10. Ibn Al Haytham’s Story • He was a mathematician and scientist from Iraq. • Offered to use his skills to visit Egypt and build a dam to stop the Nile from flooding the land. • When he arrived, he realized the task was too difficult for him and backed down. • To avoid getting killed by the Caliph Ruler, he pretended to be insane. • The Caliph felt sorry for his “insanity” and instead of killing him, he decided to lock him in a house for 10 years and called him “Majnoon”. Me Just Loco!!!

  11. Ibn Al Haytham’s Story • During those 10 years, he conducted many experiments on light and human vision. • Wrote his book in that time period. Greatest science textbook of all time. • Invented the first camera….Yes, Actually!

  12. He was inspired by Galen’s work. Then took Galen’s research to the next level!

  13. He Proved that humans and animals do NOT have built in lasers coming out of our eyes to help us see things. • Remember that was the leading theory of the time. Seemed Legit at the time. Pythagoras

  14. He proved instead that we see things when light from a light source (Sun, flashlight, light bulb, etc) bounces off of objects and ENTERS the eye. • If no light source is present, then we see nothing. • Al Haytham proved all of this using strict scientific testing. Proper scientific testing did not exist before Al-Haytham. • The Europeans changed his name to Alhazen years later. They latinized the names of most of the Muslim Scientists to make them sound more European. They had a hard time pronouncing the Arab names.

  15. The Early Years • So, he is the first person to prove that vision is the result of light bouncing off objects and going into our eyes. • Essentially that light travels TO the eye and NOT “FROM” it – well done! • He also studied other properties of light like how rainbows work but did not have much luck! Rainbow 1 Humans 0

  16. The Early Years In about the year 1600AD, dutch scientist, WillebrordSnellius (Snell for short) discovered that light bends when travelling from air into a liquid and from liquid back into the air. He called this phenomenon, Snell’s Law of Refraction! Ibn Sahl discovered refraction 600 years before me, but I get the credit….Sooo Epic!!! Refraction! MindBlown!!!

  17. The Early Years • 16 years after Snell thought he discovered Refraction of Light, Rene Descartes writes a book about it taking credit for the discovery. It Shall be called Descartes’ Law! Thaaat’s Me..!

  18. The Early Years • Renee Descartes discovered the law of Refraction in 1637 (16 years after Snell…700 years after Ibn Sahl) and gave himself full credit. Even published a book. • He was accused of plagiarism to which he claimed that he didn’t know it was already discovered. (internet wasn’t invented yet) • Today, in English parts of the world light refraction is called Snell’s Law. • In the French parts of the world today, it is called Descartes’ Law.

  19. Actually A Man Named Ibn Sahl Discovered Refraction of Light in 970AD…over 600 years before Snellius and Descartes.

  20. Ibn Sahl 1 Snell 0 (..but we love ‘em both) Light refracts….I’m gonna be famous! Light refracts. I’m gonna be famous.

  21. Optical Devices • So what is optical device? • Any technology that uses light … simple (a mirror) to complex (telescope)

  22. Optical Devices - Microscope • First microscope believed to be built in 1595 in the Netherlands by Hans & Zacharias Jansen • First major discoveries with microscopes came from Antoine van Leeuwenhoek in the 17th century • He was among first to see bacteria, algae & red blood cells • Called them “little animalcules”

  23. Optical Devices - Microscope • His discoveries led to a whole new branch of science known as microbiology! • So how do microscopes work? • They use at least two lenses (eyepiece & objective lens) • Light shines through the specimen and passes through the objective lens which produces a large image and focuses it onto the eyepiece lens which flips the image so you can see it!

  24. Then Came Telescopes • Inventor: Hans Lippershey from the Netherlands in 1608.

  25. Optical Devices - Telescope • The key tool to astronomers – people who study stars and planets • Again, 1st one came in the 1600’s in the Netherlands by Hans Lippershey! • News of this travelled really quickly to Italian scientist Galileo • This got him pretty fired up and he invented his own telescope in 1 day! • A lot of people give Galileo credit for inventing the telescope. Always remember that Lippershey did it first. They invented what?! Take that! No one out invents me!

  26. Optical Devices - Telescope • So what was the big deal with Galileo? • He discovered craters and mountains on the moon • Saw small objects orbiting Jupiter • Saw Venus has phases just like the moon • So how is a telescope different than a microscope • Not only does it magnify images but it collects light!

  27. The Early Years • Next in line was Sir Isaac Newton(1643-1727) • He loved rainbows - specifically their colours and wondered … • Performed someexperiments with prisms! What did he discover? Where does coloured light come from? #Huh?

  28. Newton Found That White Light Breaks up into a spectrum of colors when it passes through a prism. ROYGBIV

  29. Actually, I did that experiment first! Jeez, like what does a guy have to do to earn some street cred? Ibn Al Haytham

  30. The Early Years • Now we know beams of light travel to the eyes … but how fast? • The first solid finding came from Ole Romer in 1676 but during the 1920s Albert A Michelson measured it accurately! How did he do this?

  31. The Early Years Measured Distance 34.5 KM Measured the time it took to reach the other mountain and divided the distance by time Light travels … 299 798 km/s in earth’s atmosphere!

  32. To Put Into Perspective: Light can travel around the earth 7.5 times every second.

  33. So what do we know? • We know these basic properties… • Light travels in straight lines • Light can be reflected • Light can bend • Light is a form of energy What a good test question this could be …

  34. Part 2: Behavior of LIght Shadows, Reflection, Refraction,

  35. What happens When Light Strikes An Object? Light will either: • Reflect off of it (Bounce off) • Pass through it and Refract (bend) • Become Absorbed by the object. • Or any combination of the above.

  36. Light Rays & Materials • First things first – light reflects! • Ever been window shopping or reading a glossy magazine when suddenly you cannot see what you are looking at • Chalk that one up to glare (light reflected from glassor glossy surfaces)

  37. Light Rays & Materials • Why is it that lights appear intense(bright) when you are close to the light source, and less intense when you move away from the light source? • Ibn Al Haytham proved that light travels in straight lines. • He called this the “Ray Model Of Light”. • Here is sort of what he drew to explain this.

  38. Light Rays & Materials Owww! Sorry bro … I think I figured this out!! #Yolo!

  39. Light Rays & Materials Yup … #Swag That’s better right?!

  40. Light Rays & Materials Shadows: Light hits object, cannot go further. Object between the light and our eyes … the lack of light is a shadow!

  41. Light Rays & Materials • So knowing that about light what about different materials? • Transparent: allows light to pass through so an object on the other side can be seen clearly!

  42. Light Rays & Materials • Translucent: allows some light to pass through but not all of it

  43. Light Rays & Materials Opaque: These materials do not allow any light to pass through them at all. Shadows are created behind them.

  44. REFLECTION

  45. Light Rays & Materials Look at your text book. It is visible, we can see it … but how? Why? Luminous vs. Non-luminous! Non-Luminous: Does not produce light Luminous: Produces light So what though?

  46. Light Rays & Materials Light from luminous sources reflects (bounces off) other objects (like your textbook) and this reflected light is how we see everything around us. Need proof? • Try to see when the lights are off. Light bulbs are luminous and without them on there is no light to bounce and see!

  47. I conducted a few scientific tests to prove that we only see objects when light bounces off those objects and enter into our eyes. I really did prove Pythagoras, Archimedes, and Euclid wrong. Haraaam, they did not know any better. #So Lit

  48. Light & Reflection There are two types of reflection… RegularReflection: light rays hit a smooth surface and reflect back the same as they hit. The image is perfectly clear as if it did not reflect at all Same angle Same angle 45o 45o

  49. Light Rays & Materials Diffuse Reflection: Light rays strike an uneven surface and each individual light ray comes off at a different angle

  50. Law of Reflection Rays that are incoming are known as incident rays Quite simply the shiner and smoother a surface the better the reflection the incident rays produce Plane mirrors (flat mirrors) provide the clearest reflection

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