lab_27 - Coulombs Law of Electrostatic Force Introduction...

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Coulomb’s Law of Electrostatic Force Introduction: The objective of this experiment is to investigate and verify Coulomb’s law for the electrical force between two point charges (simulated using two small conducting spheres). Additionally, the method of charging by induction will be explored. Figure 1: Setup for the Coulomb's Law of Electrostatic Force experiment showing the Coulomb's Force Law kit, (guide block sphere, suspended sphere, chamber), and the vinyl strip and wool square used to charge the guide block sphere. Equipment: Coulombs Force law set-up and kit including cotton & wool squares, Polyethylene, white vinyl strips , PC computer with Excel software package. Typically the apparatus will be already set-up for you. Please be very careful the set-up is delicate. Some features of the set-up are: 1. 2 guide blocks with coated pith balls attached that will slide in and out of the unit. 2. 1 coated pith ball attached to monofilament hung and centered up in the unit. 3. A mirror and scale attached to the back of the unit to eliminate measurement errors due to parallax. 4. Top cover to eliminate air currents. If the equipment is not already setup when you arrive, you will need to complete this step. Theory:
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The electrical interaction between two charged particles is described in terms of the forces exerted between them. In 1783, Augustin Coulomb conducted the first quantitative measurements of these forces. He used a very sensitive torsion balance to measure the forces between two “point charges”, that is charged bodies whose dimensions are small compared to the distance between them. Coulomb found that the electrical force between two point charges is: Directly proportional to the product of the charges, inversely proportional to the square of the distance between them and always acts along a line joining the two charges . Mathematically we can express the magnitude of this force as, , 2 2 1 r q q k F = (1) where k is the coulomb constant and has a value of 9x10 9 N m 2 /C 2 , q 1 and q 2 are the charges on point charges 1 and 2 respectively and r is the distance between the two charges. In order to understand Coulomb’s Law we need to note a few additional properties of electrical charge. 1. There are two types of charge; we call them positive and negative. Like charges repeal, unlike charges attract. 2. Charge is quantized, that is we can not isolate any smaller amount of charge than the charge of a proton (positive) or electron (equal in magnitude to the charge on a proton, but negative). 3. Charge is conserved. We can physically move it around, but we can not create nor destroy it. 4. All matter is made of charged particles. Typically the positive and negative charges are present in equal numbers. When we say something is charged we mean it possesses a slight imbalance in the number of positive and negative charges.
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