electrostatics

# electrostatics - Electrostatics Electric charge...

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Unformatted text preview: Electrostatics Electric charge Conservation of charge Insulators & conductors Charging objects Electroscopes Lightning Van de Graff generators Equilibrium problems Grounding Static electricity Coulomb’s law Systems of charges Electric Charge • Just as most particles have an attribute known as mass, many possess another attribute called charge. Charge and mass are intrinsic properties, defining properties that particles possess by their very nature. • Unlike mass, there are two different kinds of charge: positive and negative. • Particles with a unlike charges attract, while those with like charges repel. • Most everyday objects are comprised of billions of charged, but usually there are about the same number of positive charges as negative, leaving the object as a whole neutral. • A charged object is an object that has an excess of one type of charge, e.g., more positive than negative. The amount of excess charge is the charge we assign to that object. Conservation of Charge Charged particles can be transferred from one object to another, but the total amount of charge is conserved. Experiments have shown that whenever subatomic particles are transferred between objects or interact to produce other subatomic particles, the total charge before and after is the same (along with the total energy and momentum). Example: An object with 5 excess units of positive charge and another with 2 units of excess negative charge are released from rest and attract each other. (By Newton’s 3 rd law, the forces are equal strength, opposite directions, but their accelerations depend on their masses too.) Since there is no net force on the system, their center of mass does not accelerate, and they collide there. As they “fall” toward each other, electric potential energy is converted to kinetic energy. When contact is made charge may be exchanged but they total amount before and after must be the same. After the collision the total momentum must still be zero. +5-2 +1.5 +1.5 Before After Total charge: +3 Total charge: +3 Conservation of Charge: β-decay • The stability of the nucleus of an atom depends on its size and its proton-neutron ratio. This instability sometimes results in a radioactive process known as β-decay. • A neutron can turn into a proton, but in the process an electron (beta particle) is ejected at high speed from the nucleus to conserve charge. • A proton can turn into a neutron. In this case the beta particle is an positron (an antielectron: same mass as an electron but a positive charge) to make up for the loss of positive charge of the proton. • In either case, charge, momentum, and energy are conserved. SI unit of Charge: the Coulomb • Just as we have an SI unit for mass, the kilogram, we have one for charge as well. It’s called the coulomb , and its symbol is C....
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## This note was uploaded on 11/17/2011 for the course PHYS 121 taught by Professor Burgeson during the Fall '11 term at BYU.

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electrostatics - Electrostatics Electric charge...

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