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Ohm’s Law and Resistivity

Ohm’s Law and Resistivity. Current. “Flow” of charges per second. Actual speed of an electron is called the “drift speed”. Conceptual Current. E. Current Equation. Conductivity and Resistivity. The ability of a material to conduct charges is measured by σ which is the conductivity.

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Ohm’s Law and Resistivity

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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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