Lecture 04 - Electric charge. Coulombs law

# Lecture 04 - Electric charge. Coulombs law - ACT Blowing...

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1 Lecture 4 Electric Charge Coulomb’s Law ACT: Blowing across a U-tube A U-tube is partially filled with water. A person blows across the top of one arm. The water in that arm: A. Rises slightly B. Drops slightly C. It depends on how hard is the blowing. The air pressure at A is lower where the air is moving fast. This is how atomizers work! The facts When some objects are rubbed with fur, tissue paper, certain fabrics, etc, they sometimes attract or repel each other. The repulsive/attractive force depends on the distance between the objects, on the materials used on how hard you rub used, on how hard you rub… DEMO: Rods, balloons… The proposed model Benjamin Franklin proposed that with the rubbing, objects acquired some kind of “ electric charge ”. There are two types of electric charge, which he called positive and negative . The force works in the following way: equal charges repel each other opposite charges attract each other the force gets weaker as the distance between the charged objects increases

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2 Structure of matter Later on it was established that matter is made of electrons, protons and neutrons. neutrons have no charge so we won’t worry about them protons are positive and are more or less fixed in their position electrons are negative and some of them are more of less free to move around. Most of the time, # of protons = # of electrons, so objects are neutral. Charging an object When you rub a rod with a fur, a fraction of the surface electrons in one object is transferred to the other object. - + + + - - + - - Negative Example: Gain (loss) of electrons is equivalent to loss (gain) of protons.
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## This note was uploaded on 09/21/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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Lecture 04 - Electric charge. Coulombs law - ACT Blowing...

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