1. Current Resistance Electric Power & Energy

2. Voltage (V) Electric potential difference between 2 points on a conductor Sometimes described as “electric pressure” that makes current flow Supplies the energy of the circuit Measured in Volts (V) using a voltmeter

3. Current (I) The rate of flow of charges through a cross section of a conductor Needs a complete closed conducting path to flow Ends of the conducting path must have a potential difference (voltage) Measured with an “ammeter” in amps (A) named for Ampere – French scientist One ampere (A) is charge flowing at the rate of one coulomb per second past a point in the circuit.

4. Current (I): Current flows when a potential difference exists between two points in the circuit. A resistor is any device which converts the PE of the charge flow into other energy forms. High V Low V

5. Resistance (R) The “electrical friction” encountered by the charges moving through a material. Depends on material, length, and cross- sectional area of conductor Measured in Ohms (Ω) Where: R = resistance, l = length of conductor, A = cross-sectional area of conductor, ρ = resistivity of conducting material

6. Factors Affecting Resistance The length L of the material. Longer materials have greater resistance. The length L of the material. Longer materials have greater resistance. The cross-sectional area A of the material. Larger areas offer LESS resistance. The cross-sectional area A of the material. Larger areas offer LESS resistance. The temperature T of the material. The higher temperatures usually result in higher resistances. The temperature T of the material. The higher temperatures usually result in higher resistances. The kind of material. Iron has more electrical “resistivity” than a geometrically similar copper conductor. The kind of material. Iron has more electrical “resistivity” than a geometrically similar copper conductor.

7. Resistivity ( ρ ) Property of material that resists the flow of charges (resistivity, ρ, in Ω●m) The inverse property of conductivity Resistivity is temperature dependent…as temperature increases, then resistivity increases, and so resistance increases.

8. Ohm’s Law A relationship between voltage, current, and resistance in an electric circuit  Not really a “law” – just a relationship V = potential difference (voltage) in volts I = electric current in amperes (amps, A) R = resistance in ohms (  ) (a constant)

9. Electromotive Force - emf Power lines Battery Wind generator A source of electromotive force (emf) is a device that uses chemical, mechanical or other energy to provide the potential difference necessary for electric current.

10. Using water flow in a pipe to represent current flow Low pressure Pump Water High pressure Valve Water Flow Constriction Source of EMF Resistor High potential Low potential Switch R I + - The emf source (pump) provides the voltage (pressure) to force charges (water) through electric resistance (constriction).

11. Electric Power (Watts) This is the amount of power “dissipated” (lost) from the resistor as heat. (“Joule heating”)

12. Electric Energy Electric energy can be measured in Joules (J) or Kilowatt hours ( kWh ) for Joules use Power in watts and time in seconds for kWh use Power in kilowatts and time in hours