Light and Optics

1. Light and Optics

2. Unit 8: Light and OpticsChapter 23: The Physical Nature of Light • 23.1 Electromagnetic Spectrum • 23.2 Interference, Diffraction, and Polarization • 23.3 The Dual Nature of Light

3. Key Question: What is the electromagnetic spectrum? 23.1 Investigation: The Electromagnetic Spectrum Objectives: • Research one type of wave that is part of the electromagnetic spectrum. • Prepare a poster containing the information they discover. • Make an oral presentation to share their findings with the class.

4. Electromagnetic waves • If you could shake the magnet up and down 450 trillion times per second, you would make waves of red light with a frequency of about 450 THz. • Light and radio waves are waves of electromagnetism.

5. Electromagnetic waves • If you switch electricity on and off repeatedly, the oscillating electricity makes an electromagnetic wave. • This is exactly how radio towers make radio waves.

6. The electromagnetic spectrum • Light, like sound and heat, is a form of energy. • The visible lightwe see is part of the electromagnetic spectrum.

7. Electromagnetic spectrum • The entire range of electromagnetic waves, including all possible frequencies, is called the electromagnetic spectrum. • This spectrum includes both visible light and invisible waves: • radio wave • microwaves • infrared light • ultraviolet light • X-rays • gamma rays

9. Wavelength and Frequency of Light • Because the wavelength of light is so small, scientists measure it in nanometers. • One nanometer (nm) is one billionth of a meter (0.000000001 m).

10. Frequencies and wavelengths of light • Since color is related to energy, there is a direct relationship between color (energy) and frequency and an inverse relationship between color (energy) and wavelength.

11. Electromagnetic wave speed • All electromagnetic waves travel at the same speed in a vacuum, the speed of light—3 × 108 m/s. • When moving through a material, the frequency of light stays the same.

12. Index of refraction • The index of refraction (n) for a material is the ratio of the speed of light in a vacuum to the speed of light in that material.

13. Low-energy electromagnetic waves • We classify the energy of electromagnetic waves by comparing it to the energy it takes to remove an electron from an atom. • Low energy waves, like visible light, do not have enough energy to break most chemical bonds: • Radio wavesare the lowest-frequency waves. • Microwavesrange in length from 1 mm to 30 cm. • Infrared wavesinclude wavelengths from 1 mm to about 700 nm.

14. High-energy electromagnetic waves • Ultraviolet light has enough energy to remove electrons and to break chemical bonds. • X-raysare high-frequency waves that are used extensively in medical and manufacturing applications. • Gamma rays are generated in nuclear reactions, and can strip the innermost electrons out of an atom.

15. Unit 8: Light and OpticsChapter 23: The Physical Nature of Light • 23.1 Electromagnetic Spectrum • 23.2 Interference, Diffraction, and Polarization • 23.3 The Dual Nature of Light

16. Key Question: What are some ways light behaves like a wave? 23.2 Investigation: The Wave Nature of Light: Polarization Objectives: • Use a string to demonstrate the behavior of a light wave. • Explain the interaction of polarizers, using the wave theory of light.

17. Diffraction and shadows • Like sound and water waves, light shows interference, diffraction and polarization. • Diffraction occurs when a wave passes through an opening not too much wider than the wavelength of the wave. • Observing diffraction with light is evidence that light is a wave.

18. Diffraction and shadows • You can see diffraction in a shadow cast by a sharp edge with light from a laser. • The edge of the shadow has ripples in it. • The ripples are caused by diffraction.

19. Young’s double slit experiment • In 1807, Thomas Young proved light was a wave when he showed that two beams of light could interfere with each other.

20. Light is a wave • The bright bands in an interference pattern are where the light waves from both slits are in phase at the screen (constructive interference). • The dark bands appear where the light waves reach the screen out of phase (destructive interference).

21. Diffraction gratings • A diffraction gratingactually a series of thin parallel grooves on a piece of glass or plastic. • When light goes through a diffraction grating, each groove scatters the light so the grating acts like many parallel slits.

22. Spectrometers • A spectrometer is a calibrated diffraction grating used to create a spectrum. • The spectrometer has a scale that allows you to read different wavelengths of light directly from the pattern of light made by the grating.

23. Polarization • The orientation of light is called its polarization. • Only transverse waves can have polarization.

24. Polarizers • A polarizeris a material that allows light of only one polarization to pass through it. • Light with a single polarization is called polarized light.

25. Applications of polarization • Polarized sunglasses reduce glare because they selectively absorb light with horizontal polarization while letting other light through.

26. Applications of polarization • Images on a LCD (liquid crystal display)are made using polarized light. • Each liquid crystal window can be electronically controlled to act like a polarizer, or not.

27. Unit 8: Light and OpticsChapter 23: The Physical Nature of Light • 23.1 Electromagnetic Spectrum • 23.2 Interference, Diffraction, and Polarization • 23.3 The Dual Nature of Light

28. Key Question: How does light fit into the atomic theory of matter? 23.3 Investigation: The Particle Nature of Light: Phosphorescence Objectives: • Explore the quantum theory of light. • Experiment with a photoluminescent material

29. Energy, color and light • The lowest-energy photons we can see are the ones that appear red to our eyes. • White light is a mixture of photons with a range of energy.

30. Energy and intensity of light • The intensity of light is a combination of both the number of photons and the energy per photon. • To make a red light with an intensity of 100 W/m2 takes a lot more photons than it does to make the same intensity with blue light.

31. Energy and intensity of light • If glow-in-the-dark plastic is exposed to light, it stores some energy and releases the energy later by giving off light. • The process of releasing stored light energy is called photoluminescence. Glow-in-the-dark plastic demonstrates that a single atom only absorbs a single photon at a time.

32. Light and atoms • Almost all atoms absorb and emit light. • For most atoms, the absorption and emission of light happens in less than one-millionth of a second.

33. Cinematographers, ophthalmologists, optical engineers, and computer graphic designers all play a role in the development of modern 3-D movie technology. To create the illusion of three-dimensions on a flat screen, each eye must receive its own separate image of the movie, from a slightly different perspective, mimicking the way your eyes take in a real three-dimensional scene. How 3-D Movies Work