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UNIT 8 Light and Optics

UNIT 8 Light and Optics. ConcepTest 35.1 Reflection. 1) the Moon is very large 2) atmospheric conditions are just right 3) the ocean is calm 4) the ocean is wavy 5) motion of the Moon.

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UNIT 8 Light and Optics

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  1. UNIT 8Light and Optics

  2. ConcepTest 35.1 Reflection 1) the Moon is very large 2) atmospheric conditions are just right 3) the ocean is calm 4) the ocean is wavy 5) motion of the Moon When watching the Moon over the ocean, you often see a long streak of light on the surface of the water. This occurs because:

  3. ConcepTest 35.1 Reflection 1) the Moon is very large 2) atmospheric conditions are just right 3) the ocean is calm 4) the ocean is wavy 5) motion of the Moon When watching the Moon over the ocean, you often see a long streak of light on the surface of the water. This occurs because: When the water surface changes, the angle of incidence also changes. Thus, different spots on the water can reflect the Mooninto your eyes at different times. Follow-up: Where else does this occur?

  4. Tuesday February 14th Light and Optics

  5. Tuesday, February 14 HAPPY VALENTINE’S DAY!! TODAY’S AGENDA • Characteristics of Light • Hw: Practice A (even) p449 UPCOMING… • Wed: Flat Mirrors • Thurs: Curved Mirrors Concave • Fri: NO School • Mon: Curved Mirrors Convex • Tue: Problem Quiz #1 • Color and Polarization

  6. Chapter 13 Light and Reflection

  7. Characteristics of Light James Clerk Maxwell • 1831 – 1879 • Electricity and magnetism were originally thought to be unrelated • in 1865, James Clerk Maxwell provided a mathematical theory that showed a close relationship between all electric and magnetic phenomena

  8. Characteristics of Light More of Maxwell’s Contributions • Electromagnetic theory of light • Kinetic theory of gases • Nature of Saturn’s rings • Color vision • Electromagnetic field interpretation • Led to Maxwell’s Equations

  9. Characteristics of Light Maxwell’s Starting Points • Electric field lines originate on positive charges and terminate on negative charges • Magnetic field lines always form closed loops – they do not begin or end anywhere • A varying magnetic field induces an emf and hence an electric field (Faraday’s Law) • Magnetic fields are generated by moving charges or currents (Ampère’s Law)

  10. Characteristics of Light Maxwell’s Predictions • Maxwell used these starting points and a corresponding mathematical framework to prove that electric and magnetic fields play symmetric roles in nature • He hypothesized that a changing electric field would produce a magnetic field • Maxwell calculated the speed of light to be 3x108 m/s • He concluded that visible light and all other electromagnetic waves consist of fluctuating electric and magnetic fields, with each varying field inducing the other

  11. Characteristics of Light Heinrich Rudolf Hertz • 1857 – 1894 • First to generate and detect electromagnetic waves in a laboratory setting • Showed radio waves could be reflected, refracted and diffracted • The unit Hz is named for him

  12. Characteristics of Light Electromagnetic Waves, Summary • A changing magnetic field produces an electric field • A changing electric field produces a magnetic field • These fields are in phase • At any point, both fields reach their maximum value at the same time

  13. Characteristics of Light Electromagnetic Waves are Transverse Waves • TheEand Bfields are perpendicular to each other • Both fields are perpendicular to the direction of motion • Therefore, EM waves are transverse waves

  14. Characteristics of Light The Spectrum of EM Waves • Forms of electromagnetic waves exist that are distinguished by their frequencies and wavelengths c = ƒ λ • Wavelengths for visible light range from 400 nm to 700 nm • There is no sharp division between one kind of EM wave and the next

  15. Characteristics of Light The EM Spectrum • Note the overlap between types of waves • Visible light is a small portion of the spectrum • Types are distinguished by frequency or wavelength

  16. Characteristics of Light Notes on The EM Spectrum • Radio Waves • Used in radio and television communication systems • Microwaves • Wavelengths from about 1 mm to 30 cm • Well suited for radar systems • Microwave ovens are an application

  17. Characteristics of Light Notes on The EM Spectrum • Infrared waves • Incorrectly called “heat waves” • Produced by hot objects and molecules • Readily absorbed by most materials • Visible light • Part of the spectrum detected by the human eye • Most sensitive at about 560 nm (yellow-green)

  18. Characteristics of Light Notes on The EM Spectrum • Ultraviolet light • Covers about 400 nm to 0.6 nm • Sun is an important source of uv light • Most uv light from the sun is absorbed in the stratosphere by ozone • X-rays • Most common source is acceleration of high-energy electrons striking a metal target • Used as a diagnostic tool in medicine

  19. Characteristics of Light Notes on The EM Spectrum • Gamma rays • Emitted by radioactive nuclei • Highly penetrating and cause serious damage when absorbed by living tissue • Looking at objects in different portions of the spectrum can produce different information

  20. Characteristics of Light • Illuminance decreases as the square of the distance from the source. • The rate at which light is emitted from a source is called the luminous flux and is measured in lumens (lm).

  21. END

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