The mystery of Light Rahul Saravanan - PowerPoint Presentation

1. The mystery of LightRahul SaravananGR1000201

2. IndexWhat is light?Cool facts about lightHow did I make the single slit and double slit experiment?ObservationsResultsWhy did we observe the results we did?If light is proved to be only wave-natured, then why do people also refer to light to be particle-natured?Conclusion2

3. What is Light? We are able to see things only because of it… but what is it?Page

4. Light is often defined as an Electromagnetic wave (EM wave) or the medium of illumination that makes sight possible. Currently, the accepted theory for light is it is dual-natured. Both wave and particle natured.The idea of light as a wave emerged in 1690 when Dutch mathematician-astronomer Christiaan Huygens formulated the first detailed wave theory of light. In context to this, he was also able to derive the laws of reflection and refraction.What is light? 4

5. Christian Huygens, a Dutch Mathematician-Astronomer proposed the wave theory of light in 16905

6. But, the wave theory was contradicting with the theory of light being particle natured, which was proposed by Isaac Newton in the 1660s. As Newton was more popular, the theory of light made of particles was accepted more widely than the wave theory.And experiment conducted by an English scientist Thomas Young in 1807 called the double slit experiment also seemed to show that light was wave natured.This resulted in an intense debate over which was the true nature of light.Continuation: 6

7. Isaac newton, a scientist popular for his laws of motion, proposed that light behaves like wave7

8. It was only in 1905, when Albert Einstein proposed that light had a dual nature. He proved it by explaining the photoelectric effect which can only be proved if light was particle natured. Louis de Broglie, a French scientist, proposed in 1924 that light and other particles at the atomic and subatomic level, have both particle and wave-like properties.ContinuationLouis De Broglie, the French scientist who proposed the wave-particle duality theory8

9. Funny how the we don’t “see” the facts about the most basic parts of our lifeCool Facts about light

10. Obviously, the number one position for cool facts on light is occupied by its dual nature. While the duality isn’t limited to light, it’s constituents, the photons, were the first particles used to explain the dual nature.Light is a type of EM radiation that is only visible to us in the spectrum of 400nm – 700 nm. This means, there are other regions of the radiation which are completely invisible to us. The region below 400nm is called ultraviolet(UV) radiation and above 700nm is called the infrared(IR) radiation.The speed of light is considered the theoretical limit of the maximum speed of an object. It travels at a speed of 299,792 Kilometers/second. The fastest human made object, a space probe called the Parker solar probe, was launched in 2018 and travels at around 0.064% the speed of light which is in no way a small amount. It’s cost is a whopping $1.5 Billion!!!Facts:10

11. Parker Solar Probe, The fastest Man-made object, with a recorded speed of 246960 km/hr or roughly 0.064% the speed of light. Nasa announced its cost to be $1.5 billion11

12. An Interesting experiment that verifies wave-particle dualityqUaNtuM mEcHanIcS at home!Page

13. It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do. ~Albert Einstein 13

14. Apparatus UsedA Paper cutterPaperAluminum FoilThin Copper wireScaleClass 2 LaserInsulation tapeExperimentation! Pics of items used14

15. Take a paper cutter and make 1 thin slit on an aluminum foil. Here aluminum is used since it is easy to cut a precise and tiny slit on it.Stick insulation tape on the slit such that the width of the slit is almost the width of hairStick the aluminum foil onto a paper that has a window cut into it big enough for the aluminum foil.Stick the paper onto the edge of your table such that the slit on the aluminum foil is visible clearly and protruding. Switch of all lights and point a laser at the slit that was made on the foil.Steps for single slit experiment:15

16. My Single Slit Experiment Setup1m Single Slit2m Single Slit16

17. Take a paper cutter and make 2 thin slits around 0.5 to 1mm apart on an aluminum foil. If making slits is not possible, use a thick copper wire to act as a separator to make it act as 2 separate slits.Stick electric tapes on both sides of the wire such that only a small window is available for light to pass through on the slits.It is better to stick the aluminum foil onto a paper that has a window cut into it big enough for the aluminum foil.Stick the paper/foil onto the edge of your table such that the slit on the aluminum foil is visible clearly and protruding. Switch of all lights and point a laser at the double slit that was made on the foil.Double slit experiment:17

18. My Double Slit Setup1m Double Slit2m Double Slit18

19. Observation and Results19

20. Records of observations for single slit:Distance of source from screenDistance between bright spots1 meter5 mm2 meter11 mm20

21. Records of observations on double slit:Distance between Screen and LaserDistance between bright spots1m4 mm2m6-8 mm21

22. On the single slit experiment, we observed a diffraction pattern appearing on the screen (wall) where there was a maximum brightness spot called the diffraction maximum on the center and other minor secondary bands, which reduce in brightness, on either side of the diffraction maximum. This is contradicting with the expectation for the light to form only one point on the screen.On the double slit, we noted that an inference pattern with dark and light bands which were appearing contrary to what we expected, which was getting 2 bright spots only. Why did this happen?What did we observe?22

23. Unexpected observations!Why did we observe what we did?

24. The inference pattern we get from the double slit can only be explained if light behaves like a wave.When light passes through the 2 slits, concentric circles originating from these slits are also formed. These 2 circles intersect and create those inference patterns just as you’d expect waves to act. Just like how waves in water intersect and create patterns. Explanation for the observations:24

25. Light and water both display similar wave-like properties25

26. In the case of the single slit, diffraction patterns are formed because light bends around edges just as waves do. For better understanding, we can consider all the light in the aperture or the slit width as point sources. This way, just like in the double slit experiment, we have concentric circles originating from each point source.See image in next page for comparison of light intensities between the 2 patterns we found.More Explanation!26

27. Diffraction Patterns formed with single and double-slits27

28. If light was only wave-natured then why do we have wave-particle duality theory?28

29. Through the experiment that was done by Thomas Young, it was proved that light was wave-natured. But, it didn’t mean light was ONLY wave natured.Light was proved to be particle natured by Albert Einstein when he explained how the photoelectric process worked. When a beam of light is aimed at a metal, the photons collide with the metal. If the photon’s frequency is sufficient enough to knock out the electrons, the collision produces the photoelectric effect. This is only possible if the beam of light is made of particles.To resolve this dilemma, Louis de Broglie hypothesized that all objects at the atomic or sub-atomic level exhibit both wave-like and particle-like properties.Why is light also considered to be particle-natured?29

30. The Photoelectric effect which was only explainable if light was particle-natured30

31. All things must come to an end… Even the very atoms that make up our body (albeit they have a MUCH longer lifespan!)Conclusion

32. After 2 centuries of intense debate, light was finally accepted to be dual-natured. But this isn’t just the case for light. Scientists have theorized that all particles at the scale of atoms or small (quantum level) are dual natured. Wave-particle duality is also a part of quantum mechanics. How? Quantum mechanics is a body of science dealing with the bizarre behavior of particles at a very small scale like photons, electrons and other fundamental particles. In classical mechanics, any object is said to be in a specific place at a specific time. Any object is also said to be in a definite state.Conclusion:32

33. But, when we look at quantum objects, we realize that these objects aren’t in any single place at a particular time or in a definite state. They exist in multiple locations at the same moment, having a probability of existing in any given location. They also can exist in multiple states at times.This is true for light as well. Light can be described as either a wave or a particle. This isn’t possible in classical mechanics where objects have to be in a definite state. This makes the wave-particle duality theory part of quantum mechanicsConclusion33

34. Thank you for reading through!I hope the presentation helped with your understanding of the weird nature of light34