Photon Concept of Light (Grade 12 ).pptx

Photon Concept of Light (Grade 12 ).pptx

1. Photon Concept of Light

2. The Photon Theory of Light Light is composed of photons. Based on the photon theory of light, a photon is a discrete bundle of electromagnetic energy moving at the speed of light, has no rest mass but has momentum and carries energy. This energy is given to an electron upon their collision, which causes it to move up to the next energy level.

3. The photoelectric effect refers to the ejection of electrons from a surface of a metal in response to light directed to the metal. Albert Einstein proposed that light consisted of individual photons, which interacted with the electrons in the surface of the metal. For each frequency or color of the incident light, each photon carried energy.

4. More electrons are ejected upon the increase in incident light. Increasing the frequency of light would increase the energy of the ejected electrons. The energy carried by a photon is directly proportional to its frequency. The arrangement of the visible spectrum of light shows that red color has the least frequency, which means it also has the least energy.

5. Color Spectra Colors are not innate to objects. They give off light that appears as colors . Colors only exist in the human visual system and is determined by frequencies. When light reaches the eye, it falls into a receptor cell at the back of the eye or retina and gives signals to the brain, which interprets the image with colors .

6. The Colors in Light Sunlight separates into different colors , called visible spectrum, as it passes through a prism. The spectrum consists of colors of the rainbow: red, orange, yellow, green, blue, indigo and violet colors .

7. Red, Green, and Blue are the basic colors in light and therefore film. The secondary colors , Yellow, Cyan, and Magenta, are combinations of these. You can mix tertiary colors (orange, violet, etc) and all other colors from there as well.

8. Addition of Primary Color of Light Red + Blue = Magenta Red + Green = Yellow Blue + Green = Cyan Red + Green + Blue = White

9. Color of Opaque Objects When white light falls on an object which does not transmit light, one of the three things happens: 1. All of the colors in white light may be reflected, in which case the object will appear white. 2. Some of the colors may be reflected, in which case the object appears colored . 3. All the colors are absorbed by the object, in which case the object appears black. For example, a red shirt looks red because it absorbed the wavelengths of light from violet/blue end of the spectrum. A leaf of a plant is green because it reflects green light.

10. Reflects 1.Red 2.Orange ROYGBIV Appears 3. Red Orange Paper absorbs YGBIV

11. Ultraviolet Radiation Different colors of light have photons of different energies. Based on the frequency and wavelength in a visible light, red has low frequency and long wavelength, which means that it contains less energy. Blue, on the other hand, has high frequency and short wavelength, which means it contains more energy. Beyond the visible light, the ultraviolet light has greater frequency and shorter wavelength, which means it carries greater energy than the visible light. This explains why we easily get sunburned under the ultraviolet rays of light than under the visible light.

12. How Light Acts as Wave and a Particle

13. The Experimental Evidence Showing that Electrons can Behave like Waves.

14. DOUBLE-SLIT THOUGHT-EXPERIMENT In Feynman's double-slit thought-experiment, a specific material is randomly directed at a wall which has two small slits that can be opened and closed at will- some of the material gets blocked and some passes through the slits, depending on which ones are open.

15. Based on the pattern that is detected beyond the wall on a backstop- which is fitted with a detector- one can discern whether the material coming through behaves as either a wave or particle. When particles are fired at the wall with both slits open, they are more likely to hit the backstop in one particular area, whereas waves interfere with each other and hit the backstop at a number of different points with differing strength, creating what is known as an interference pattern.

16. In 1965, Feynman popularized that electrons- historically thought to be particles- would actually produce the pattern of a wave in the double-split experiment. Unlike sound waves and water waves, Feynman highlighted that when electrons are fired at the wall one at a time, an interference pattern is still produced.

17. THE PHOTOELECTRIC (EFFECT) EXPERIMENT Photoelectric effect, phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it. In a broader definition, the radiant energy may be infrared, visible, or ultraviolet light, X-rays, or gamma rays; the material may be a solid, liquid, or gas; and the released particles may be ions (electrically charged atoms or molecules) as well as electrons.

18. The photoelectric effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz. In connection with work on radio waves, Hertz observed that, when ultraviolet light shines on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking takes place. This relation between light and electricity (hence photoelectric ) was clarified in 1902 by another German physicist, Philipp Lenard.

19. He demonstrated that electrically charged particles are liberated from a metal surface when it is illuminated and that these particles are identical to electrons, which had been discovered by the British physicist Joseph John Thomson in 1897.

20. Further research showed that the photoelectric effect represents an interaction between light and matter that cannot be explained by classical physics, which describes light as an electromagnetic wave. One inexplicable observation was that the maximum kinetic energy of the released electrons did not vary with the intensity of the light, as expected according to the wave theory, but was proportional instead to the frequency of the light. What the light intensity did determine was the number of electrons released from the metal (measured as an electric current). Another puzzling observation was that there was virtually no time lag between the arrival of radiation and the emission of electrons.

21. THE COMPTON SCATTERING EXPERIMENT The Compton effect is the inelastic scattering of a photon (usually X-ray or γ-ray) by an electron; when the target electron is moving, the Compton-scattered radiation is also Doppler-broadened, and its energy distribution at a given scattering angle is called Compton profile.

22. Measurements of Compton profiles of materials give information on the electron momentum density, projected along the scattering direction. The technique is particularly sensitive to the most external electronic wave functions, which describe slowly moving electrons and are responsible of the chemical bond. A closely related method which provides similar information is the study of the angular correlation in positron annihilation. When a photon is scattered by an electron, its wavelength shift can be obtained from energy and momentum conservation laws.

23. By classical theory, when an electromagnetic wave is scattered off atoms, the wavelength of the scattered radiation is expected to be the same as the wavelength of the incident radiation. Contrary to this prediction of classical physics, observations show that when X-rays are scattered off some materials, such as graphite, the scattered X-rays have different wavelengths from the wavelength of the incident X-rays. This classically unexplainable phenomenon was studied experimentally by Arthur H. Compton and his collaborators, and Compton gave its explanation in 1923.

24. Arthur Compton (1892–1962) showed that this behavior could be explained by assuming that the X-rays were photons (light quantum). When photons are scattered off electrons, part of their energy is transferred to the electrons. The loss of energy is translated into a reduction of frequency, which in turn leads to a lengthening of the wavelength of the scattered photons.

25. To explain the shift in wavelengths measured in the experiment, Compton used Einstein’s idea of light as a particle. The Compton effect has a very important place in the history of physics because it shows that electromagnetic radiation cannot be explained as a purely wave phenomenon. The explanation of the Compton effect gave a convincing argument to the physics community that electromagnetic waves can indeed behave like a stream of photons, which placed the concept of a photon on firm ground.

26. Beam of electrons Glows when electron strikes Fringe Pattern Exhibiting interference effects Television like screen Double-slit

27. Electron are emitted from Light shines on it Light being udes Sufficiently high frequency Light Photoelectrons

28. Photon model Of X-ray by electrons Graphite Electron in graphite Recoils in another direction Compton Effect

29. In Double-slit Thought Experiment, the screen is like a television screen and glows wherever an electron strikes it. There was pattern observed, which consists of bright and dark fringes, reminiscent of what is obtained when light waves pass through a double-slit.

30. The fringe patterns indicate that the electrons are exhibiting the interference effects associated with waves.

31. Photoelectric Effect is an experimental evidence that light consists of photons, in which electrons are emitted from a metal surface when light shines on it. The electrons are emitted if the light being used has a sufficiently high frequency.

32. When the electrons are ejected with the aid if light, they are called photoelectrons.

33. Compton Scattering Effect Experiment was conducted by the American physicist Arthur H. Compton. Compton used the photon model the scattering of X-rays by electron in graphite.

34. The phenomenon in which an X-ray photon is scattered from an electron, with the scattered photon having a smaller frequency than the incident photon, is called Compton Effect.

35. It involves the transport of energy without the transport of matter and can be described as a disturbance that travels through a medium. a. Light b. Sound c. Waves

36. .Who suggested that, like light, electrons could act as both particles and waves? a. Louise de Broglie b. Richard Feynman c.Arthur Compton

37. What phenomenon states that when a metal surface is exposed to a monochromatic electromagnetic wave of sufficiently short wavelength (or equivalently, above a threshold frequency), the incident radiation is absorbed and the exposed surface emits electrons? a. Double Slit-thought Experiment b. Compton Scattering Experiment c. Photoelectric(effect) Experiment

38. Who gave the first experimental proof of the existence of radio waves in 1887; he also discovered the photoelectric effect? a. Feynman’s Double-slit b. Louise de Broglie c. Heinrich Rudolf Hertz

39. Which principle says that sometimes electrons have the properties of particles and sometimes the properties of waves, but never both together? a. Complementarity Principle b. Uncertainty Principle c. Wave functions

40. Which phenomenon X-ray photon is scattered from an electron with the scattered from an electron, with the scattered photon having a smaller frequency than the incident photon? a. Compton effect b.Photoelectric c. Double-slit

41. . Electromagnetic waves are composed of particle-like entities called ______. a. Photoelectrons b. Photons c. Collector

42. An electron emitted from an atom by interaction with a photon, especially an electron emitted from a solid surface by the action of light. a. Photoelectrons b. Photons c. Collector

43. DISPERSION, SCATTERING INTERFERENCE AND DIFFRACTION OF LIGHT

44. Dispersion is the separation of white light into its seven color components when there is a refraction or bending of light.

45. When white light passes through a prism, it will refract two times making the separation of the colors noticeable.

46. A Prism is a piece of glass or transparent material usually triangular in shape. It allows visible light to pass through.

47. Isaac Newton first investigated dispersion by allowing white light to pass through a glass prism. He also found that if the dispersed white light were allowed to pass through another upside-down prism, white light was produced.

48. In 1637, Rene Descartes first gave a detailed explanation of the formation of rainbow by mathematically tracing the path of light in a spherical drop of water. In the primary rainbow, the outer color is red and the inner color is violet. For the secondary rainbow, the colors are reversed.

49. Light scattering is the ability of particles to absorb light and scatter it in all directions

50. Scattering of light components depends on the size of the particles or scatterers; small particles scatter components of short wavelengths (high frequency) while larger particles scatter longer wavelengths (low frequency).

51. Our atmosphere is composed of tiny particles that scatter the color components of white light and has an abundance in nitrogen and oxygen particles, which can scatter higher frequency. They scatter violet the most, followed by blue, green, and so on.

52. This selective scattering is called the Rayleigh scattering. Our eyes are more sensitive to blue frequencies of light, which is why we see the sky as blue.

53. At sunset, sunlight travels farther through the atmosphere. Longer distance would mean that much of the blue light (having shorter wavelengths) have been scattered. Leaving only yellow, orange and red (having longer wavelengths) to be scattered resulting to a red-orange sunrise or sunset.

54. Mie Scattering, happens when electromagnetic wave incident on the particles and after reflections, all range of wavelengths get reflected back equally to the atmosphere.

55. E xample of this is the clouds. Clouds appear white because the water droplets in the clouds are larger than the wavelength of light which scatter all the colors of light equally. Clouds that contain too much water droplets like rain clouds are less effective scatterers and more effective absorbers of light. Thus, rain clouds appear dark.

56. ACTIVITY 4: Scatter-Hunting DIRECTION: Determine if the underlined word or phrase exemplified in each statement is Rayleigh or Mie Scattering. _________________ 1. Joshua observes the yellow sky one-day morning. ___________________2. Jean enjoys watching the white and fluffy clouds by the window. ___________________3. Caroline is in a hurry to go home as the clouds appear dark. ___________________4. Jill and Joven feels very happy seeing the red-orange light during sunrise. ___________________5. Ping shields her eyes from the glare of sunlight.

57. ___________________6. One reason why tourists visit “Boracay Beach” is to witness the red-orange sunset. ___________________7. Karen witnesses the presence of crepuscular rays near her bedroom. ___________________8. Carole enjoys seeing the white clouds having dark bottoms over her balcony. ___________________9. Vanessa burns the dried leaves under the tree and observes that the rays of the sun pass through the smoke. ___________________10. The sky is very clear today! I love to see the blue sky.