#2 - Physics 1230: Light and Color Instructor Professor...

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Unformatted text preview: Physics 1230: Light and Color Instructor Professor Margaret Murnane CLASS 1- Waves and the Electromagnetic Spectrum Sources of Light in Nature Sources of Light in Nature Lecture 1 Light and Color for Non Scientists PHYS 1230 Describing waves Light waves - the Electromagnetic Spectrum Speed of light Waves We are familiar with waves in everyday life - waves on a rope, waves in the ocean, sound waves, shock waves x Propagating waves - rope is medium Propagating waves - air is medium rope More about Waves A wave is a propagating disturbance of some equilibrium state - for example wave on water, waves on a rope, light in vacuum etc. The medium does not have to move far - but the disturbance moves, often at some characteristic speed (e.g. cork on water) Wave on a rope Light waves Waves on a Rope http://phet.colorado.edu/new/simulations/sims.php?sim=Wave_on_a_String Concept Question - Waves on a Rope http://phet.colorado.edu/new/simulations/sims.php?sim=Wave_on_a_String The direction of motion of the rope is - A. Parallel to the propagation of the wave B. Perpendicular to the wave propagation C. Other Waves Both the waves in the flag and the ocean waves are waves that you can see - where we see the medium move. There are other kinds of waves. We cannot see these waves, but we experience them every day. These waves are called electromagnetic waves. Sound Waves Sound is also a type of wave that we cannot see. Like ocean waves, sound waves need a medium to travel through. Sound can travel through air because air is made of molecules. These molecules carry the sound waves by bumping into each other, like Dominoes knocking each other over. Sound can travel through anything made of molecules - even water! There is no sound in space because there are no molecules there to transmit the sound waves! Waves can be either Periodic or Aperiodic Periodic wave Aperiodic wave Periodic wave space Wavelength For periodic waves, we can identify a wave length , , by measuring the distance between unique points Periodic wave Periodic wave space Period and Frequency For periodic waves, we can identify a period , T, by measuring the time taken for a wavelength to pass a given point - The frequency , , is the inverse of the period i.e. = 1/ and is the number of times per second that an oscillation occurs at any fixed point in space Wavelength of a Wave What is the wavelength of the red wave? A) 1m B) 2m C) 3m meters Period of a Wave What is the period of the red wave? A) 2 millisecond B) 2 seconds C) 2 minutes meters Wavelength, Frequency, and Velocity For periodic waves, we can identify a speed , v, by speed = distance/time speed = Wavelength/Period speed = Wavelength x frequency v = Wavelength, Frequency, and Velocity For periodic waves, we can identify a speed , v, by Speed = distance/time Speed = Wavelength/Period Speed = Wavelength x frequency v = So => c = or = c / or = c / So knowing the frequency...
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#2 - Physics 1230: Light and Color Instructor Professor...

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