PHY 182 1st Edition Lecture 23Outline of Last Lecture I. ResistanceII. SuperconductivityIII. Resistance vs. ResistivityOutline of Current Lecture I. Internal ResistanceII. Power in CircuitsIII. Kirchhoff's RulesCurrent LectureInternal Resistance- Ideally, a source of emf outputs its total amount of possible voltage. However in real batteries, this is not the case.- Real batteries have finite resistance; this is called the internal resistance.- When current is flowing through the battery, the voltage is equal to the emf minus the current flowing through it multiplied by the internal resistance. This voltage is called the "terminal voltage".- The current in a circuit with internal resistance can be found using Ohm's Law, however, you must add the internal resistance to the resistance in the circuit.- For new batteries, internal resistance is very small (approximately .001 Ohms). As thebattery gets more worn out, this resistance increases.- Assume wire has zero resistance unless otherwise stated.- A voltmeter is assumed to have infinite resistance.- An ammeter is assumed to have zero resistance.Power in CircuitsThese 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.- The power of a circuit can be calculated by multiplying the voltage supplied by the battery by the current.- Power is defined as the rate at which energy is delivered to or extracted from a circuit element.- The SI unit of power is watts (1 W = 1 J/s).- The power delivered to a resistor or wire shows up as a temperature difference.Kirchhoff's Rules- The first of Kirchhoff's Rules is the Junction Rule. This states that the algebraic sum ofthe currents into any junction is zero.- A junction is defined as the meeting of 3 or more conductors.- The second rule is the Loop Rule. This rule states that the algebraic sum of potential differences in any loop is
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