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Electrical Forces & Coulomb’s Law

Electrical Forces & Coulomb’s Law. They’re Attractive & Repulsive at the Same Time. +. +. -. -. When two charges are brought together they either push away from each other or they pull towards each other. If there is no net force acting on an object, then.

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Electrical Forces & Coulomb’s Law

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  1. Electrical Forces & Coulomb’s Law They’re Attractive & Repulsive at the Same Time

  2. + + - - When two charges are brought together they either push away from each other or they pull towards each other. If there is no net force acting on an object, then Since the charges will change their motion, Newton’s First Law tells us they must have a force applied to them!!!! Newton’s Third Law tells us that the force on each charge must be equal in size but opposite in direction. They are an action-reaction pair!!!!

  3. Electric Charge • We know that there are two types of charge – positive and negative. • We know that protons are 2000 times bigger than electrons in terms of mass. • We know that even though protons are positively charged & electrons are negatively charged, protons and electrons carry the same size charge. • The size of the charge on a proton & an electron is defined in units called a Coulomb (C). • A Coulomb (C) is the unit used to measure electric charge.

  4. Electric Charge • A Coulomb of charge is very large. • It would take 6.25 X 1018 protons to make 1-C of charge. • For those of you who avoid scientific notation like the plague: It takes 6,250,000,000,000,000,000 protons to make 1-C of charge. • A proton has a charge of 1.6 X 10-19-C, an electron has a charge of -1.6X 10-19-C. • For you anti-plague people: • 1.6 X 10-19-C = 0.000 000 000 000 000 000 16-C

  5. Coulomb’s Law As a formula this looks like: Where k is called Coulomb’s Constant and is equal to 9 X 109 or 9,000,000,000. In 1875, Charles Coulomb did some experiments on the forces between electric charges. He discovered two things: 1) The size of the force depends directly with the product of each charge.. FE ~ Q1∙Q2 Where Q is the size of the charge in Coulombs. 2) The size of the force depends inversely with the square of the distance between the charges. FE ~ 1/r2 Where r is the distance between the charges.

  6. Example Find the electrical force between a 1-C charge and a 3-C charge that are 6-m apart. Q1 = 1-C Q2 = 3-C r = 6-m The (+) answer means the force is repulsive – LIKE CHARGES REPEL

  7. Example 2 Find the electrical force between a 5-C charge and a -5-C charge that are 100-m apart. Q1 = 5-C Q2 = -5-C r = 100-m The (-) answer means the force is attractive – opposite CHARGES attract

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