AS101 Lecture 13

AS101 Lecture 13 - AS101 Lecture 13 Logistics: Homework 5...

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AS101 Lecture 13 Logistics: • Homework 5 due today • Homework 6 available • Review end-of-chapter Questions • Review homework problems Last Lecture: • Energy • Tides Today’s Lecture: • Atom • Light • Light and matter MIDTERM 1 on Thursday Oct 21 In class Covers material up to last class Close Book, Notes etc. Bring calculator – No cell phones or PDAs
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Atomic model • What is atom? – Old idea - again from the Greeks – Democritus (470 - 380 BC) • The smallest object obtained after continuous and repeated “breaking” • Atom - a Greek word meaning indivisible • Modern scientists use atom-smashers and have found out that atoms are also composed of even smaller particles
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The Bohr atom • Due to Danish Physicist Neils Bohr (1885-1962) Nobel 1922 Electrons Nucleus Various “orbits” possible The orbits are well- determined
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How big are atoms?
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Atoms • Nucleus : – Protons • positively charged • Mass: 1.67 x 10 -24 g – Neutrons • No electrical charge • Electrons – negatively charged – Mass: 9.1 x 10 -28 g (about 1/1800 of protons)
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Periodic Table of the Elements atomic number = #protons atomic mass no. = #protons + #neutrons
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Fusion Powers the Sun Energy given off by one proton-proton chain reaction Mass of Proton: m p = 1.6726x10 -27 kg Mass of 4 He: m He = 6.643x10 -27 kg 4 m p – m He = 4.7x10-29 kg E = m c 2 = (4.7x10 -29 kg)(3x10 8 m/s) 2 = 4.2x10 -12 kg m 2 /s 2 = 4.2x10 -12 Joules
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Electrons can only be in certain “orbits” Energy levels for hydrogen atom - levels are quantized Not This but This
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Quantum Mechanics
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When electrons fly the coop
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Light We can use light to say something about astronomical objects’ • Composition (what is it made of) • Temperature (how hot is it) • Velocity (how fast is it moving) To understand how we do these, first we need to learn about light
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Early studies on light Galileo attempted to measure the speed of light using his pulse as a clock (early 1600) Failed, but this same technique resulted in studies on simple
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AS101 Lecture 13 - AS101 Lecture 13 Logistics: Homework 5...

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