# Lab 1 - Coulombs Law Determination Eric Tao January 21st...

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Coulomb’s Law Determination Eric Tao January 21st, 2013 Abstract In this study, we determined the dependency between the electrical force and the charge, and the force and the distance. This was done by first keeping charge as constant and recording the deflection caused by repulsion due to different separations, and then methodically decreasing charge and recording the different deflections. Thus, we conclude that the electrical force goes as F q 1 q 2 r 2 , confirming Coulomb’s Law. 1 Introduction For electrically charged particles, it has been determined by Coulomb that there is a force felt between two charged particles that goes as: F q 1 q 2 r 2 However, we wish to verify this, and experimentally determine how F varies with respect to r, the distance, and q, the charge on the particle. By using a setup for which we know the gravitational restoring force on, we took measurements of how this restoring force changes with different values of q and r. 2 Methodology For this experiment, we used two conducting balls, one suspended from two points with height l and one that we set its position. The suspended ball was allowed to swing freely through some angle θ and a distance d away from the equilibrium point was measured as its displacement. 1

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Figure A: Experimental Setup The two balls were charged by first rubbing the fixed ball in fur to charge it as much as possible, then allowing the two balls to equalize in charge by letting them touch. Although the amount of charge is arbitrary, the exact measure of charge is irrelevant. Then, we measured the distance d that the hanging ball varied from the equilibrium point. It can be proved that, for small angle θ , the gravitational restoring force is: T cos θ = mg so then T = mg cos θ We wish to find the value of T sin θ Substituting in, we find that T sin θ = mg tan θ By geometry, tan θ = d l 2 - d 2 Since in our case, l d
• Winter '13
• MarceloGleiser
• Physics, Charge, Force, Electric charge, Equilibrium point, electrical force, Coulomb’s law, gravitational restoring force

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