# Lab2 - Electrostatics Coulomb's Law Objective To learn how...

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Electrostatics: Coulomb's Law Objective: To learn how excess charge is created and transferred. To measure the electrostatic force between two objects as a function of their electrical charges and their separation distance. Apparatus: Copper sphere on rod (3, one with standing base), charging rod, capacitor, fake fur, scale, meter stick, ring stand, voltmeter, connectors and wires Introduction There are two types of electrical charge - positive and negative. Like charges (positive and positive, or negative and negative) repel each other, while unlike charges (negative and positive) attract each other. Materials through which charges are free to move, like most metals, are called conductors. Materials in which charges are not free to move, like most nonmetals, are called insulators. The charges that are mobile in conductors are negative charges – the free electrons that are not bound to any particular atoms. The charges that are static are positive charges – protons which are in the nuclei of the atoms that make up the material. Charge is neither created nor destroyed (conservation of charge). The appearance of excess charge on an object happens when charge being transferred from somewhere else.

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For instance, rubbing a piece of amber with a piece of fur results in the amber acquiring a net negative charge; however, the fur has acquired a net positive charge from the same interaction. In this experiment, you will produce excess charge by rubbing, and then transfer this charge to conducting copper spheres. The spheres are connected to insulated rods so that they can be handled without the charge leaking out. A scale on which one of the charged spheres is placed would then read heavier or lighter (giving us the Coulomb force magnitude) in the presence of another charged sphere, compared to its weight as an electrically neutral sphere. You will measure the distance between the spheres using a meter stick, and the charge on each sphere by discharging it into a capacitor, a device that stores a charge. Since the capacitor is connected to a voltmeter, you can then determine the charge that was on it from the equation: Q=CV where Q is the charge, C is the capacitance, and V is the voltage Coulomb's Law, which determines the electrostatic force between objects 1 and 2 based on their electrical charges and separation distance, is written as follows: F =k Q 1 Q 2 r 2 The constant of proportionality k has the units Newton-Meter 2 /Coulomb 2 and has the value k = 9 x 10 9 N m 2 r 2 As in gravitational forces, the electrostatic force lies along the line connecting the center of the spheres. The sign of the Coulomb force will be either be positive, denoting repulsion or negative, denoting attraction. Note that if one of the charges in the equation is negative, the force will be attractive. If both charges are negative or positive, the force will be repulsive. As mentioned before, like charges repel while unlike charges attract.
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Lab2 - Electrostatics Coulomb's Law Objective To learn how...

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