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lec18 - Physics I Class 18 Coulombs Law Rev 08-Mar-07 GB...

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18-1 Physics I Class 18 Coulomb’s Law Rev. 08-Mar-07 GB
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18-2 Forces Known to Physics (Review) There are four fundamental forces known to physics: Gravitational Force (“yesterday’s news”) Electromagnetic Force (start today) Weak Nuclear Force Strong Nuclear Force (All forces we observe are comprised of these fundamental forces. Most forces observable in everyday experience are electromagnetic on a microscopic level.)
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18-3 A New Property of Matter - Charge Charge comes in two types: positive and negative. NET charge can neither be created nor destroyed. (Principle of Conservation of Charge) However, positive and negative charges can be separated or combined. Charge is quantized – the smallest unit of charge (magnitude) in normal experience is the charge of the electron or proton, “e”. (All charges are integer multiples of this unit.) By arbitrary historical convention, the charge of an electron is negative and the charge of a proton is positive. Neutral H +e charge electron -e charge 0 charge proton
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18-4 Conservation of Charge neutron anti-neutrino 0 charge proton +e charge 0 charge electron -e charge Charge is even conserved in nuclear reactions. Here is what happens to a free neutron (outside a nucleus) in about 12 minutes: This is an example of the weak nuclear force (beta decay).
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18-5 Coulomb - A Man, A Unit, A Law Charles Coulomb, 1736-1806 Coulomb invented a delicate torsion balance with which he was able to measure the forces between charged and magnetic objects with sufficient accuracy to verify a previous conjecture that the mathematical formula for electromagnetic force should resemble the formula for gravity. The unit of charge is named after Coulomb, abbreviated C. 1.0 C = 6.24150975 × 10 +18 e 1.0 e = 1.60217646 × 10 –19 C One Coulomb is a lot of protons!
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18-6 Coulomb’s Law of Electrostatic Force ) ( r q q 4 1 F 2 2 1 0 - ε π = The meaning of each term: F : Electrostatic force on charge 1 from charge 2. 0 4 1 ε π : Electrostatic force constant = 8.98755 × 10 +9 N m 2 /C 2 1 q : Value of charge 1, positive or negative.
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