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The nature of light! What is light?! Light acts like a wave (it is an electromagnetic wave) http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=52 Light acts like a stream of particles Light is the only thing we can see Visible light is a small portion of the electromagnetic spectrum Visible light ranges in wavelength from about 400 nanometers (nm) to about 760 nm What is an electromagnetic wave?! all electrons are surrounded by an electric field a wiggling electron will wiggle the electric field a wiggling electric field will induce a wiggling magnetic field a wiggling magnetic field will induce a wiggling electric field get it? It keeps going and going! The electromagnetic spectrum! Frequency corresponds to color and energy The higher the frequency, the more energy the wave “packets” carry Highest frequency--hard gamma rays Ultraviolet--frequency just above the upper visible violet. Infrared--frequency just below visible red. Microwaves--resonant frequency with water Radio--large range of frequencies for info transmission EM Spectrum! Light as a wave! diffraction--will spread out after going through an opening if the opening is small enough refraction--will bend if entering a different medium at an angle interference--produces interference patterns just like water and sound waves do can be polarized (made to vibrate in a single plane) Light as a particle! can propagate in a straight line-(laser) is emitted in bundles called “photons” each photon is a particle-like packet, clump, discreet amount, or quantum of light energy (E=hf, h=Planck’s constant=6.62x 10-34 J s) higher intensity light (brighter) means more photons higher frequency light means more energy per photon A wave and a particle?! How can anything be a wave and a particle at the same time? Particle-wave duality violates common experience, yet is clearly evident at the microscopic level Richard Feynman said “I think I can safely say that nobody understands quantum mechanics.” Additional Tidbits! em waves travel at 3 x 108 m/s in a vacuum when em waves encounter a “medium” they get slowed down the higher the frequency the wave, the more dangerous it is, and the more dense a material it can go through all Wave Nature of Light! Young’s Double Slit Interference Experiment We will collect data in class Make all calculations on the HW sheet Read Microscopic Weirdness & answer questions Read and take notes from Giancoli section 24-3 (p. 727 – 730)