Light
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This document discusses the nature of light and summarizes the key theories about what light is. It describes light exhibiting properties of both waves and particles. The wave theory proposed by Huygens stated that light is a wave, which was supported by experiments on reflection, refraction, interference and diffraction. The particle theory was proposed by Newton, but Young's experiment on interference demonstrated light's wave properties. Maxwell's electromagnetic theory described light as electromagnetic waves that can travel through a vacuum. The quantum theory reconciled both wave and particle descriptions, explaining that light behaves as both waves and particles.
Light
- 1. 1 Nature of Light as Waves
- 2. 2 What is Light? •The natural agent that stimulates sight and makes things visible. •Electromagnetic radiation from about 390 to 740 nm in wavelength.
- 3. "Is light a wave or a stream of particles?" 3
- 4. 4 Let’s first analyze characteristics behaviors of light as a wave.
- 5. Reflection • All waves are known to undergo reflection or the bouncing off of an obstacle. 5
- 6. Refraction • Change in direction of propagation of any wave as a result of its traveling at different speeds at different points along the wave front. • All waves are known to undergo refraction when they pass from one medium to another medium. 6
- 7. Diffraction • Diffraction involves a change in direction of waves as they pass through an opening or around an obstacle in their path. 7
- 8. Interference 8 • In 1807, Thomas Young (1773-1829) did the most convincing experiment demonstrating that light is a wave. • A beam of light fell on a pair of parallel, very thin slits in a piece of metal. • After passing through the slits, the light fell on a screen. • A pattern of alternating bright and dark bands formed is called an interference pattern.
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- 10. Interference • Wave interference is a phenomenon that occurs when two waves meet while traveling along the same medium. 10
- 11. Polarization • Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming un-polarized light into polarized light is known as polarization. 11
- 12. Polarization • The fact that light shows polarization tells us that light is a transverse wave. • Transverse waves are waves that cause the particles of the medium to vibrate perpendicularly to the direction of motion. 12
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- 14. 14 Polarization Hint • Light vibrates in all directions. • A polarizing filter acts like a picket fence. It only lets certain direction vibrations pass through it. • Therefore, if you pass light through two of them you can completely block the light from passing through. • HOW?
- 15. 15 Polarization
- 16. 16 Now what about the particle-like behavior?
- 17. 17 The photoelectric effect is observed when light of a certain frequency strikes a metal and ejects electrons.
- 18. 18 Phenomenon Can be explained in terms of waves. Can be explained in terms of particles. Reflection Refraction Interference Diffraction Polarization Photoelectric effect
- 20. 20 • Light is a special type of wave. • What we know as light or VISIBLE LIGHT is actually a type of something called ELECTROMAGNETIC RADIATION. • So, what is electromagnetic radiation and electromagnetic waves?
- 21. 21 Electromagnetic Radiation • When something creates energy it also emits radiation. Depending on the amount of energy, the object will emit different types of electromagnetic radiation. • When we studied mechanical waves, they were all transferred through a medium. What medium is light transferred through?
- 23. 23 Electromagnetic Waves • Electromagnetic waves are waves that do not need a medium to propagate through. • But what is creating the disturbance? What is emitting this energy?
- 24. ELECTRONS 24
- 25. 25 Electromagnetic Waves • Electromagnetic waves are everywhere. • Light is only a small part of them – Radios – TVs – Microwaves – Light (Visible/UV/InfraRed) – Radiation – Lasers – CD/DVD players – X-Rays
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- 27. 27 Electromagnetic Waves • Electrons in materials are vibrated and emit energy in the form of photons, which propagate across the universe. • Photons have no mass, but are pure energy. • Electromagnetic Waves are waves that are made up of these “photons”.
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- 29. The Corpuscular Theory • Created in the seventeenth century by Sir Isaac Newton • States that light emitted by luminous objects consist of tiny particles of matter called corpuscles. When corpuscles hit a surface, each particle is reflected. • Thought that light traveling from air into water will increase the speed, while light entering water will decrease the speed. 29
- 30. The Wave Theory • Discovered by Christian Huygens, a Dutch scientist, also in the seventeenth century • States that light is emitted in a series of waves that spread out from a light source in all directions. These waves are not affected by gravity. • Furthermore, he disagreed with Newton and said that light traveling from air to water will decrease the speed, and vice versa. Huygens was proved later to be correct. • 100 years later, Englishman Thomas Young completely disproved the corpuscular theory by showing that light waves can interfere with each other. 30
- 31. The Electromagnetic Theory • Discovered in the nineteenth century by James Maxwell • Proposed that light waves do not require a medium for transmission. • Light waves posses electrical and magnetic properties and can travel though a vacuum. Light waves are a part of a larger family of electromagnetic waves and make up the electromagnetic spectrum. 31
- 32. The Quantum Theory • Discovered by Max Planck, German scientist in 1900 • Stated that light waves travel as separate packets of energy called quanta or photons. • Merged the subjects of the Corpuscular, Wave, and Electromagnetic Theories together. • Later, it was proved that the correct and most accurate theory was the Quantum Theory. 32
- 33. • Quantum Theory explains that light has both properties of waves and particles thus, light is both wave and particle. 33
- 34. Both particles and waves?!? What the hell?! © 2003 Mike Maloney 34
- 35. © 2003 Mike Maloney 35
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- 37. Yes! Malapit na recess!!! © 2003 Mike Maloney 37