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Understanding Ohm’s Law and Resistivity in Electric Current

Learn about Ohm's Law, resistivity, conductivity, drift speed, temperature effects on resistance, and more in electrical circuits with practical examples.

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Understanding Ohm’s Law and Resistivity in Electric Current

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  1. Ohm’s Law and Resistivity

  2. Current “Flow” of charges per second Actual speed of an electron is called the “drift speed”

  3. Conceptual Current E

  4. Current Equation

  5. Conductivity and Resistivity The ability of a material to conduct charges is measured by σ which is the conductivity. The inverse of conductivity is ρ which is the resistivity. The unit of resistivity is the Ω·m.

  6. Ohm’s Law Many materials exhibit a linear relationship between I and V for a given R. Such materials are referred to as “ohmic” and follow the equation:

  7. Ohmic Non-ohmic V V slope = R I I

  8. Resistance and Temperature Resistance of a conductor directly related to Temperature

  9. Example A 10 m long copper wire conducts 4A of current when 12V of potential are applied to it at a temperature of 20ºC. The temperature coefficient for copper is 3.9x10-3. What is the amount of current the wire will conduct if the temperature drops to -10ºC and the same 12V is applied to it?

  10. R vs T (normal conductor)

  11. R vs T (Superconductor) TC

  12. Meissner Effect http://en.wikipedia.org/wiki/Meissner_effect

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