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1/16/2014 Resistance Ohm’s Law Peter Mathys ECEN 1400 Resistance and Conductance • The amount of resistance to current is measured in ohms (Ω) and is represented by the letter R. • The reciprocal of resistance is conductance measured in siemens (S) and represented by G = 1/R. Graphic Aid for Ohm’s Law • In most materials current is passed through the movement of free electrons. • Moving electrons occasionally collide with the atoms making up the material. • These collisions cause the electrons to lose energy, which is converted to heat. • The property of a material that restricts the flow of charge (electrons) is called resistance. Ohm’s Law • Georg Simon Ohm (1787 – 1854) determined experimentally that voltage v, current i, and resistance R are related by • Using conductance G = 1/R Resistors in Series 1 1/16/2014 Resistors in Parallel 3 Resistors in Parallel Absorbed Power Maximum Power Rating Power Rating Example Voltage Division • Find maximum v and i for 1 kΩ, ¼ W resistor. • Maximum v: • Maximum i: 2 1/16/2014 Current Division 3