PHY 102 1nd Edition Lecture 15 Outline of Last Lecture I. WavesII. Sound WavesIII. Light WavesIV. IntensityV. InterferenceVI. DiffractionOutline of Current Lecture I. ReviewII. Blue BookIII. ElectromagnetismIV. CoulombCurrent LectureI. Reviewa. v = λfb. Interference = distance between sources (holes) < 10λc. Diffraction = size of hole (aperture) < 10λII. Blue Book Problems (waves, interference, diffraction)III. Electromagnetisma. Modern electricity began with the work of William Gilbert, a 16th century physician, who showed that light objects such as pieces of paper could be electrifiedb. By the middle of the 18th century, machines were invented that could electrify certain objects indefinitelyc. Two kinds of electricity were discoveredi. Positiveii. Negatived. At about the same time, the conducting property of metals was also discoveredi. In 1734, the record distance for electrical transmission via conductors was383 metersIV. CoulombThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. The end of the 18th century saw the discovery of the electrostatic force law by Charles Coulombb. Like charges repel; unlike charges attracti. Electric charge is denoted by q and measured in Coulomb (C)c. The attractive or repulsive force between two electric charges q1 and q2 obeys the Coulomb lawd. Fe = (keq1q2)/r2 --> ke = 9x109i. Looks exactly like gravitational force (Fg = (Gm1m2)/r2 --> G = 6.67x10-11), but is much strongere. Two electrons attract each other gravitationally, but repel each other electricallyf. Fe/Fg = 4.17x1042 = ratiog. The electric force is represented by over a million times the visible universe!h. Gravity dominates celestial physics because celestial bodies are electrically neutrali. Electricity holds matter together: atoms, molecules, solids, liquids, gases, and
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