PHY 182 1st Edition Lecture 22Outline of Last Lecture I. Nuclear Fusion ReactionsII. Electric CurrentOutline of Current Lecture I. ResistanceII. SuperconductivityIII. Resistance vs. ResistivityCurrent LectureResistance- For some materials (especially metals), current density is nearly directly proportional to the electric field. This relationship is called "Ohm's Law".- Resistivity is equal to electric field divided by current density.- A perfect conductor has zero resistivity.- A perfect insulator has infinite resistivity.- Resistivity of conductors vs. insulators is approximately a factor of 1022.- A material that follows Ohm's law (ideal material), it is called an "Ohmic" or "linear" material.- Resistivity is temperature dependent.- The resistivity of a metallic conductor nearly always increases with increasing temperature.Superconductivity- Superconductivity is a character exhibited by only certain materials (like mercury) and usually only occurs at very low temperatures.- Conductivity is the reciprocal of resistivity.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Resistivity will slowly decrease as the temperature decreases then at some critical temperature, the resistivity will suddenly drop to zero.Resistance vs. Resistivity- Electric field and current density are hard to measure, but current and voltage are not.- We define resistance as the relationship between V and I, R=V/I.- An alternate form of Ohm's law is V=IR.- Be sure to remember that voltage causes current, not the other way around.- The SI unit of resistance is the Ohm, which is equal to 1V/1A.- Resistivity is a property of the material; resistance depends on property and
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