Resistance and Ohm’s Law Alessandro VoltaAndre Ampere Georg Ohm
Resistance – a measure of how much a material resists the flow of electrons – SI unit is Ohms (Ω) Greek letter omega) – Good conductors have a low resistance Ex: copper Ohms – Poor conductors have a high resistance Ex: dry human skin 500,000 Ohms
Factors that Affect Resistance in a Wire 1. Resistance increases as the length of the wire increases
2. Resistance increases as the width decreases - wire gauge describes its width American Wire Gauge (AWG)
3. Resistivity of a material affects resistance. Material Resistivity (ohmmeter) Silver 1.59 x Copper 1.7 x Gold 2.4 x Aluminum 2.8 x Tungsten 5.6 x Carbon 3.5 x 10 5 Polyethylene Glass Hard Rubber 10 13
R = _L_ A is resistivity L is length A is cross-sectional area (width) imulation/resistance-in-a-wire
Analogy: Water experiences more resistance as pipes get smaller and longer, so current decreases.
Ohm’s Law Resistance = Voltage Current R = V I More commonly seen in this form: V = IR
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