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VI Resistance - the opposition of current in a conductor A. Ohm’s Law 1. On a V vs. I graph the slope of the graph is resistance. 2. Conductors whose resistance is constant over a range of V and I are said to obey ohm’s law or are ohmic. 3. Ohm’s Law V=IR 4. R is resistance in ohm’s (Ω) B. Factors Affecting the Resistance 1. Different materials have different resistances, called resistivity based on physical and chemical properties of the material (values found in reference tables). 2. As the length of wire increases, the resistance increases (more collisions) 3. As the cross sectional area of the wire increases, resistance decreases 4. As temperature increases, resistance increases. If you cool a conductor to its critical temperature the resistance drops to zero ~ superconductor. 5. Formula for resistance R=ρL/A (go through each term and its units)