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REVIEW SHEET STATIC AND DYNAMIC ELECTRICITY 1. COULOMB’S LAW: Formula for calculating the force between two point charges. Force repulsive if both charges are the same sign, attractive if they are different signs F kq1q2 r2 k = Coulomb constant = 9 x 109 Nm2/C2 q1 - charge on the first point q2 - charge on the second point charge r - distance between the charges 2. ELECTRIC FORCE: F qE q - magnitude of the charge E - Electric field strength 3. WORK DONE (Electric Energy): In moving a charge in an electric field: 4. VOLTAGE AND WORK (Electric Energy): V W q W – Work (Energy) V- Voltage (potential difference) q - charge Work = Joules eV’s W qV Charge x Coulombs Elementary charges Voltage Volts Volts 5. ELEMENTARY CHARGE: a. qe - charge on an electron = - 1.6 x 10 -19 coulombs (fundamental unit of charge) b. qp - charge on a proton = 1.6 x 10-19 coulombs (fundamental unit of charge) c. Like a penny - no smaller coin - charge cannot exist in a smaller unit. d. 1 Coulomb = 6.25 x 1025 elementary charges 6. TOTAL CHARGE: a. Qt -Total charge (C) b. N - Number of elementary charges c. qe – Elementary Charge = - 1.6 x 10 -19 QT N q 7. METHODS OF TRANSFERING CHARGE: a. Induction - no contact between objects. b. Contact - rubbing objects together. 8. ELECTRIC FIELD SURROUNDING: a. positive charge - emanates from it b. negative charge - terminates on it c. two positive charges - field diverges d. two negative charges - field diverges e. one positive and one negative charge f. between two parallel plates g. surrounding a sphere 9. Electron Volts (eV’s) (Elementary charges) x (volts) W qV 1eV 1.6 x10 19 J 9. DYNAMICS (MOVING CHARGES), CURRENTS - Current = amount of charge/time I q t I - Current, measured in amperes (A), an ampere is a coulomb/second. q - Charge (C) t - Time it takes for the charge to flow (sec.) 10. WORK AND POTENTIAL - To move a charge in an electric field requires work, to calculate: V W q V - Potential difference (voltage) W - Work (J) joules q - magnitude of the charge C 11. ELECTRON VOLT: A unit of energy (eV) which is defined as the amount of energy, or work, needed to accelerate an electron through a potential difference of 1 volt. 1eV 1.6 x10 19 J 12. CIRCUITS AND OHM’S LAW - Ohm’s Law relates the current, voltage, and resistance in a circuit. a. V - voltage (volts) V b. R - resistance (ohms) c. I - current (amperes) A V IR 13. RESISTANCE OF WIRE: Depends upon 3 quantities: a. P - A constant, which depends upon the type of material the conductor, is made. Ex: gold and silver are good conductors; offer little resistance to the flow of electrons, p would be small. b. L - Length of the conductor, longer length more resistance. c. A - Area, more cross-sectional area, less resistance. 14. POWER: The rate at which energy is used in the circuit l R A V2 I 2R P IV R 15. ELECTRIC ENERGY: Product of Power and time. V2 t E Pt IVt I Rt R 2 16. SERIES CIRCUIT: a. Current same in each element: IT=I1=I2=I3 b. Sum of the potential drops equals the total potential. (That of the battery): VT=V1+V2 +V3 c. Rt = R1 + R2 + R3 + ….. add resistors to find the total. 17. PARALLEL: a. Voltage the same across each element: Vt = V1 = V2 = V3 b. Sum of the currents equals the total current: It = I1 + I2 + I3 c. For two resistors in parallel: 1/RT = 1/R1+1/R2+1/R3