Waves and Light
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Waves and light are discussed, including characteristics of waves, the nature of light, and its speed of 3x10^8 m/s. Light behaves as both a wave and particle - as an electromagnetic wave with electric and magnetic fields, and as photons. The photoelectric effect is explained as the ejection of electrons from surfaces illuminated by ultraviolet light.
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Waves and Light
- 1. Module 5 Part 2 Waves and Light Dr. Paul H. Comitz pcomitz@live.com
- 2. Agenda Characteristics of Waves The Nature of Light The Speed of Light Light as a wave Light as a Particle: The Photoelectric Effect: Lab Photo Electric Effect http://phet.colorado.edu/en/simulation/photoelectric
- 3. Course Modules # Module Weeks Reading Quiz 1 Newton's laws 1 Ch 4,5 * 2 Conservation of Energy and Momentum 2,3 Ch 6,7,8 Quiz 1 3 Thermodynamics 4,5 Ch 12,13,14 4 Electromagnetism 6,7 Ch 17,18 Quiz 2 5 Waves, Sound, and Light 8,9 Ch 16, 20, 21 Quiz 3 6 Modern Physics 10 Ch 23 Final Exam * it is strongly recommended you read chapters 0 - 3
- 4. Module 5 Reading: Chapters 16,20,21 Chapter 16 - Wave Motion and Sound Chapter 20 - Light Chapter 21 Reflection and Refraction Exercise 5, due start of week 10 (4%) Quiz 3 In class tonight Labs Waves (3.75%) Quantum Theory (3.75%) (Photoelectric Effect) Final Exam In class 8/23
- 5. Review: Characteristics of Waves Energy may be transferred through wave motion Amplitude Wavelength Frequency Period
- 6. Characteristics of Waves Period time to complete one vibration Example: Pendulum makes 2 vibrations in 1 second. Frequency is 2 Hz. Period of vibration is 12 second. Example: AM Radio frequency is 660 kHZ Period 1.5 ms = 1frequency period = 1period frequency
- 7. If the frequency of a particular wave is 20 Hz, its period is A. 50 milliseconds B. 20 seconds. C. more than 20 seconds. D. none of the above Vibrations and Waves CHECK YOUR NEIGHBOR
- 8. If the frequency of a particular wave is 20 Hz, its period is A. 50 milliseconds B. 20 seconds. C. more than 20 seconds. D. none of the above Explanation: Note when = 20 Hz, T = 1/ = 1/(20 Hz) = 1/20 second = 50 ms. Vibrations and Waves CHECK YOUR ANSWER
- 9. The Nature of Light Straight Line Propagation Reflection Mirror/smooth surface Rough surface Refraction Bending of light as it passes through boundary of two media
- 10. The Nature of Light Wave Theory Each point on a wave front can be regarded as new sources of small wavelets that spread out uniformly in the forward direction at the same speed Particle Theory Light is made up of streams of particles called photons Einstein Light behaves as both a particle and a wave
- 11. The Nature of Light: Speed of Light Initially though to be instantaneous 1920: Measurement method developed by Albert Michelson Measured 299,792,458 m/s Often abbreviated: 3 x 108 m/s In US units: 186,000 mi/s Recall v = l/T = lf l is wavelength T is period f is frequency
- 12. The Nature of Light: Speed of Light Average speed of light through different materials vacuumc (300,000,000 m/s) atmosphereslightly less than c (but rounded off to c) water0.75 c glass0.67 c, depending on material diamond0.41 c
- 13. The Nature of Light: Refraction Refraction bending of light when it passes from one medium to another caused by change in speed of light
- 14. Refraction Illusions caused by refraction Objects submerged in water appear closer to the surface.
- 15. The Nature of Light: Reflection Law of reflection The angle of reflection equals the angle of incidence.
- 16. The Nature of Light: Reflection Diffuse reflection when light strikes a rough or irregular surface and reflects in many directions an undesirable circumstance is the ghost image that occurs on a TV set when TV signals bounce off buildings and other obstructions
- 17. Light as an Electromagnetic Wave Electromagnetic waves are produced by moving electric charges Electric charges have an electric field Moving electric charges create a magnetic field
- 18. Electromagnetic Spectrum Electromagnetic spectrum classification of electromagnetic waves according to frequency lowest frequency of light we can see appears red highest frequency of light we can see appears violet higher frequency of light is ultravioletmore energetic and causes sunburns beyond are X-ray and gamma ray no sharp boundary between regions
- 20. The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A. radio waves. B. microwaves. C. visible light. D. gamma rays. Electromagnetic Spectrum CHECK YOUR NEIGHBOR
- 21. The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A. radio waves. B. microwaves. C. visible light. D. gamma rays. Electromagnetic Spectrum CHECK YOUR ANSWER
- 22. Which of these is fundamentally different from the others? A. sound waves B. light waves C. radio waves D. X-rays Electromagnetic Spectrum CHECK YOUR NEIGHBOR
- 23. Which of these is fundamentally different from the others? A. sound waves B. light waves C. radio waves D. X-rays Explanation: All are electromagnetic waves except sound, which is a mechanical wave. Electromagnetic Spectrum CHECK YOUR ANSWER
- 24. Light as a Particle: The Photoelectric Effect Einsteins view on light as a stream of particles, bundles of energy (photons) photons interact with matter one at a time high-energy photons dislodge electrons from certain metals Einstein was awarded the Nobel Prize in Physics in 1921 for his paper on the Photoelectric effect Photon A particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero mass
- 25. The Photoelectric Effect Quantum Physics Quantization the idea that the natural world is granular rather than smoothly continuous Quantum any elemental particle that makes up matter or carries energy
- 26. Light As a Particle: The Photoelectric Effect A model for how matter radiates Light is a stream of photons each with a particular quantum of energy high-energy photons dislodge electrons from certain metals energy in each quantum is proportional to the frequency of radiation E ~ f, or with Plancks constant h, E = hf h = 6.62 x 10-34 J s
- 27. The Photoelectric Effect high-energy photons dislodge electrons from certain metals
- 28. Summary The Nature of Light Straight Line Propagation Reflection Refraction Speed of light c = 3 x 108 m/s Light behaves as both a wave and a particle Electromagnetic wave B and E fields Particles Photons Photoelectric effect Ejection of electrons from surfaces illuminated by UV light