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Unformatted text preview: Phys 133 – General Physics III Midterm 1 Review I. Electricity A. Electric charges and the Electric Force 1. Fundamentals The fundamental unit of charge ( e ) is carried by protons (+) and electrons (-). The total charge on an object is q = ( N p- N e − ) e. An object is neutral if it has no net charge ( q = 0). Ionization is the removal of electrons from an atom. Charge conservation : charge is neither created nor destroyed. 2. Insulators and Conductors Insulators are materials in which charges are immobile. The charge remains wherever it is placed on the object. Conductors are materials in which charges are free to move. a) Charging In insulators, charges remain in place. In conductors, charges are free to move. Since they are like charges, they repel and move as far away from each other as possible. Any net charge on a conductor lies on the surface. Electrostatic equilibrium is the condition where the charges are at rest and there is no net force on any charge. b) Polarization : the slight separation of positive and negative charge in an object (or atom). Electric dipole : a configuration of two opposite charges with a slight separation between them (think of a water molecule). 3. Coulomb’s Law describes the force acting between two point charges: F 1on2 = F 2on1 = k | q 1 || q 2 | r 2 , where k = 1 4 πǫ The magnitude of the force force on each charge in the pair is equal due to Newton’s Third Law. M. Ouellette, 22 April 2007 Page 1 of 5 • For opposite charges, the force is directed toward the other particle. • For like charges, the force is directed away from the other particle. Forces act on a charge only when there is at least one other charge present....
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