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
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?
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
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
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
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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