summer electrostatics packet.doc - Electrostatics IB 12 1...

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IB 12 1 Particle Mass Electric Charge Electron m e = 9.110 x 10 -31 kg q = -e q = -1.60 x 10 -19 C Proton m p = 1.673 x 10 -27 kg q = +e q = +1.60 x 10 -19 C Neutron m n = 1.675 x 10 -27 kg q = 0 q = 0 C Electrostatics 1) electric charge: 2 types of electric charge: positive and negative 2) charging by friction: transfer of electrons from one object to another 3) positive object: lack of electrons negative object: excess of electrons Conservation of Electric Charge: The total electric charge of an isolated system remains constant. 4) Types of materials: a) Conductors : materials in which electric charges move freely (e.g. metals, graphite) b) Insulators : materials in which electric charges do not move freely (e.g. plastic, rubber, dry wood, glass, ceramic) c) Semiconductors : materials with electrical properties between those of conductors and insulators (e.g. silicon) d) Superconductors : materials in which electrical charges move without resistance (e.g. some ceramics at very low temperatures) Properties of Atomic Particles e = elementary unit of charge (magnitude of charge on electron) e = 1.60 x 10 -19 C DO: 1. A balloon has gained 2500 electrons after being rubbed with wool. What is the charge on the balloon? What is the charge on the wool? DO: 2. A rubber rod acquires a charge of -4.5 μC. How many excess electrons does this represent?
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IB 12 2 Electric Force (Electrostatic Force, Coulomb Force) Coulomb’s Law: The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to square of the distance between them, and directed along the line joining the two charges. NOTE: +-F denotes direction of force not sign of charge 1 2 2 0 1 2 2 0 1 4 4 e e q q r q q F r F   1 2 2 e F q q k r k = Coulomb constant (electrostatic constant) k = 8.99 x 10 9 N·m 2 C -2 k = 1/ 4πε 0 ε 0 = permittivity of free space = 8.85 x 10 -12 C 2 N -1 m -2 Coulomb Force Point charge: a charged object that acts as if all its charge is concentrated at a single point Alternate formula for Coulomb force: DO: Use the Coulomb force to estimate the speed of the electron in a hydrogen atom.
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IB 12 3 The Principle of Superposition The net electric force acting on a charged particle is the vector sum of all the electric forces acting on it. DO 1. Determine the net electrostatic force on charge q 1 , as shown below. DO 2. Where can a third charge of +1.0 µC be placed so that the net force acting on it is zero? DO 3. Three point charges of -2.0 µC are arranged as shown. Determine the magnitude and direction of the net force on charge q 1 .
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IB 12 4 Electric Field Electric field: a region in space surrounding a charged object in which a second charged object experiences an electric force Test charge: a small positive charge used to test an electric field Electric Field Diagrams (DO ALL 7) 1. Positively charged sphere 2. Positive point charge 3. Negative point charge Radial Field: field lines are extensions of radii 4. Two positive charges 5. Two negative charges 6. Two unlike charges Properties of Electric Field Lines 1. Never cross 2. Show the direction of force on a small
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