PHY 102 1nd Edition Lecture 15 Outline of Last Lecture I Waves II Sound Waves III Light Waves IV Intensity V Interference VI Diffraction Outline of Current Lecture I Review II Blue Book III Electromagnetism IV Coulomb Current Lecture I II III IV Review a v f b Interference distance between sources holes 10 c Diffraction size of hole aperture 10 Blue Book Problems waves interference diffraction Electromagnetism a Modern electricity began with the work of William Gilbert a 16 th century physician who showed that light objects such as pieces of paper could be electrified b By the middle of the 18th century machines were invented that could electrify certain objects indefinitely c Two kinds of electricity were discovered i Positive ii Negative d At about the same time the conducting property of metals was also discovered i In 1734 the record distance for electrical transmission via conductors was 383 meters Coulomb These 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 Coulomb b Like charges repel unlike charges attract i Electric charge is denoted by q and measured in Coulomb C c The attractive or repulsive force between two electric charges q 1 and q2 obeys the Coulomb law d Fe keq1q2 r2 ke 9x109 i Looks exactly like gravitational force Fg Gm1m2 r2 G 6 67x10 11 but is much stronger e Two electrons attract each other gravitationally but repel each other electrically f Fe Fg 4 17x1042 ratio g The electric force is represented by over a million times the visible universe h Gravity dominates celestial physics because celestial bodies are electrically neutral i Electricity holds matter together atoms molecules solids liquids gases and plasmas
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