1. 4.3 Notes Resistance in Electrical Systems

2. Properties of Materials Conductors Have a large ability to conduct electric current They contain many free electrons Metals are good conductors Temperature influences resistance of the flow What happens to the energy when resistance is present in electrical systems? Insulators

3. Variables and Units of Electricity Voltage (potential difference)- the ability to accelerate an electric charge between two points in an electric field. Measured in VOLTS Current - the rate of flow in a conductor. Measured in AMPERES Resistance - measure of the ability of an electrical device to oppose flow of charge through a device Measured in OHMS ( Ω )

4. Types of Circuits Series A circuit with only one path for the current to flow R SERIES = R 1 + R 2, R 3 +… Parallel

5. Ohm’s Law V = IRVoltage = (current) (resistance) I = V / RCurrent = (voltage) / (resistance) R = V / IResistance = (voltage) / (current) Resistivity - a property of a material that describes its ability to resist flow of electric charge Resistivity is a physical property of individual materials and is influenced by temperature. R = ρ (L/A) Measured in ( Ω  m)

6. Resistors R = (First digit * 10 + second digit) (multiplier)