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Prepare your scantron: Use • Fill in your name and fill the bubbles under a pencil, your name. not a pen! • LAST NAME FIRST, First name second • Put your 4-digit code instead of “IDENTIFICATION NUMBER”. --- (The last 4 digits of your OleMiss ID.) Pass/Fail on Tuesday 6:00 pm!! Question # 1: answer A Setup: Question # 2: answer B Question # 3: answer E Reading assignment Chapter 5 (Light), pp. 137-164 Please take a moment to mute your cell phone! The physics of light Light … is an electromagnetic wave: • … is a wave pattern of electric and magnetic fields • … propagates in vacuum • … has wavelength (blue: 400 nm, red: 700 nm) 0.4 mm 0.7 mm Learn units of distance! 1 mm = millimeter Millimeter (size of ant) 1000 mm = 1 mm Micrometer (size of a germ) 1000 nm = 1 mm Nanometer (size of ten atoms) Speed of light c = 300,000 km/s: Discovered by: Olaus Roemer (1675) Watch 07JupiterMoonDance.mov Light takes • a few minutes/hours to move around in the solar system • years or more to go from star to star • Eclipses of Jupiter’s moons come a few minutes late when Jupiter is on the far side of its orbit. • Reason: light needs extra time to reach us. • Conclusion: light needs 9 minutes to traverse the Sun-Earth distance. Olaf Römer The electromagnetic spectrum Light has a wavelength: l Wavelength of light means color: • Blue has short wavelength • Red has long wavelength What is beyond blue? These are colors of light invisible to the eye. Bluer than blue is UV (ultraviolet) - even shorter wavelength Redder than red is IR (infrared) - even longer wavelength And what is beyond those wavelengths? (A prism breaks up white light into colors.) The full spectrum Prism Radio | Infrared | Visible Radio antenna Slit White light | Ultraviolet X-ray| g -ray Eye / Telescope Need spacecraft (Far UV, X-ray, g-ray) Need spacecraft They all move with the same speed c = 300,000 km/s Questions coming … Question 4 30 29 12 13 14 15 16 17 18 20 21 22 23 24 25 26 27 28 10 11 8765432109 19 Which one is moving fastest? A Radio waves B X-rays C Visible light D Laser E The same sec Next question coming … Question 5 30 29 12 13 14 15 16 17 18 20 21 22 23 24 25 26 27 28 10 11 8765432109 19 What is the difference between red and blue light? A Intensity. B Speed. C Wavelength. D Blue is composite, red is not. E Red is existence of light, blue is lack of light. sec Next question coming … Question 6 How many of the following types of “light” penetrates the atmosphere? • Radio waves • Far IR • Regular light • Far UV • X-rays 45 25 30 35 40 12 13 14 15 16 17 18 19 10 11 20 4321087659 sec A1 B 2 C3 D4 E5 Next question coming … Question 7 30 29 12 13 14 15 16 17 18 20 21 22 23 24 25 26 27 28 10 11 8765432109 19 How was the speed of light measured for the first time? sec A In an experiment with a laser beam. B By the time delay the astronauts’ answer came from the Moon. C Observing the moons of Jupiter. D By measuring the radar signal reflected by the Moon. E By measuring the time light takes to arrive to us from another galaxy. Recall: Structure of Chemistry cannot change the nucleus, only bind atoms into molecules atomchemical properties. Isotopes: same number of p and e, different n. Same Examples: H: Deutron: He: 1p 1p 2p 0n 1n 2n 1e 1 e (same as H but heavier) 2e Photons Einstein’s discovery: Red l = 720 nm, E = 1.7 eV Blue l = 420 nm, E = 3 eV UV l = 100 nm, E = 12 eV X-ray l = 1 nm, E = 1200 eV light comes in chunks (photons) each photon has E=1240/l energy in electron-volts (eV) in nm’s Enough to destroy most atoms Destroys everything if strong Turn in your scantron now personally!