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lecture 4 100902 - Light Light It is against the honor code...

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Unformatted text preview: Light Light It is against the honor code to “click” for someone elseviolators will loose all clicker pts. We have observed light 1. travels in straight lines 2. reflects 3. refracts It also 4. transmits energy from one place to another HITT RF Remote Login Procedure: Two theories could explain these phenomena. The radio channel number for this room is “09” (zero, nine). It is STRONGLY recommended to login your remote for every class just to be sure it is on the correct radio channel and working before class. 1. 2. 3. 4. PRESS AND HOLD THE DOWN ARROW KEY until the GREEN light on the remote turns RED. PRESS THE “0” KEY and you will see the RED light flash GREEN. PRESS THE “9” KEY and you will see the RED light flash GREEN. PRESS AND RELEASE THE DOWN ARROW KEY again and you will see the red light search for the receiver, if it BLINKS GREEN MULTIPLE TIMES you are logged in. Thanks to friends at Texas A&M U for help with the slides What were the two theories of light in the 1600s and who were their main advocates? • • • • • A. B. C. D. E. Corpuscular-Newton and Wave-Huygens Corpuscular-Huygens and Wave-Newton Gravity-Newton and String-Weinberg Force-Newton and Wave-Huygens Wave-Aristotle and Gravity-Newton The WAVE THEORY, The WAVE advocated by advocated Christian Huygens Christian and Robert Hooke, and Robert said that light was a wave. The PARTICLE (corpuscular) THEORY, advocated The PARTICLE advocated by Isaac Newton and later by Pierre Laplace, said Laplace said that light was made up of a stream that of tiny particles called corpuscles. The more popular theory was the particle theory σιφϕρνµ The σιφϕρνµ of the because φϕερυισ reputation of Isaac Newton. . because φϕερυισ φνευ µδυ ωο υιδφ νσευφ ϕφκγλβ The debate among the two sides continued through the mid 1800’s. Newton’s particle theory could easily explain the straight line travel of light, reflection, and energy transmission, but had trouble explaining refraction. 1801 interference of light was discovered interference 1816 - diffraction of light (actually observed in the 1600’s but not given much significance) was explained using interference principles Newton’s explanation of refraction required that light must travel faster in water than in air. light faster Huygen’s wave theory could easily explain reflection, energy transmission, and refraction, but had difficulty explaining the straight line travel of light. The wave theory’s explanation of refraction required that light must travel slower in water than in air. Neither phenomena could be explained satisfactorily by the particle theory. The final blow to the particle theory came in 1850 when theory 1850 when Jean Foucault discovered that Jean light traveled faster in air than in water. It was then widely accepted that light was a wave, but what kind of wave? In 1865, James Maxwell In James developed ideas began by developed Michael Faraday into a Michael series of equations that proposed the electromagnetic wave theory. It proposed electromagnetic said that light was a type of e/m wave: a periodic said e/m wave: periodic disturbance involving electric and magnetic forces. foucault light demo Foucault put a tube of water in the light beam and showed that light slowed down in the water! Newton was wrong! The whole universe is composed of SHOs SHO is system with linear restoring force to original shape/position Mass/spring Frequency f = 1ω = T 2π ωms = k m g L Types of Waves – Transverse λ X direction (space/not time) Longitudinal or compression wave λ Chapter 14 Wave motion-Wave velocity c c c t Oscillators make Waves All waves carry energy and momentum Each part of spring moves ⊥To wave motion Like AM radio Pendulum ωp = In 1885, Heinrich Hertz In 1885 Heinrich experimentally confirmed the e/m theory of light. the e/m Tuning Forks produce single frequency sound c = λƒ Always true: Light-transverse Sound-longitudinal Any wave Most waves need a medium-Except light λ • As the tuning fork vibrates, a succession of compressions and rarefactions spread out from the fork • A sinusoidal curve can be used to represent the longitudinal wave – Crests correspond to compressions and troughs to rarefactions Categories of Sound Waves • Audible waves – human hearing: Normally between 20 Hz to 20,000 Hz • Infrasonic waves – Frequencies are below the audible rangeEarthquakes or car stereos • Ultrasonic waves – Frequencies are above the audible range Dog whistles Middle C on the piano is 440 Hz. The speed of sound in air is about 330 m/s. What is the wavelength of this sound wave? 1. 2. 3. 4. 4.7 m 1.3 m 0.75 m 0.87 c = λƒ Always true: Light-transverse Sound-longitudinal Any wave ...
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