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May 20, 2016 Resistance of a Wire 1. What is the cause of resistance in a wire? Collisions between conduction electrons and lattice ions Symbol: Factors Units: Symbol Unit Less Resistance More Resistance Relationship Length Cross-sectional Area Resistivity Temperature Resistance of a Wire What type of wire is the best conductor (least resistance)? Formula for a conducting wire at a constant temperature . . . May 20, 2016 Resistance of a Wire 2. What are the properties of wire that is the best conductor (has the least resistance)? short, wide area, good conductor 3. What are the properties of wire that is the worst conductor (has the most resistance)? long, thin, bad conductor 4. To make a wire with the lowest resistance, what material would you use? Highest resistance? silver - best conductor 5. What is the resistance of a copper wire 2.0 meters long with a cross-sectional area of 6.4×10-8 m2? 6. a) What is the resistance of a nichrome wire 12 meters long with a diameter of 2.7×10-4 meter? b) if the diameter of the wire above is doubled, what is its resistance? May 20, 2016 Simple Circuits and Schematics Schematic: diagram using symbols to represent circuit elements For each circuit shown below, draw a corresponding schematic diagram using appropriate Circuit Symbols 1. Actual Circuit Schematic Diagram of Circuit 2. Actual Circuit Schematic Diagram of Circuit May 20, 2016 Water Analogy for a Simple Circuit Electric Circuits 1. For the electric circuit shown, what is the potential (voltage) at: 2. For the electric circuit shown, what is the potential difference from: May 20, 2016 Electromotive Force (emf): conversion from some other form of energy into electrical energy voltage rise, potential increase Potential difference (pd): conversion from electrical energy into some other form of energy voltage drop, potential decrease Resistance in an Electric Circuit Variable: V I R Quantity: Units: Type: Electrical resistance: ratio of applied potential difference to current Formula: May 20, 2016 Resistance in an Electric Circuit 3. What is the resistance of a small appliance that draws 3.00 A at 120 Volts?