Lecture_9

Lecture_9 - 20.8 Series and Parallel Circuits Now lets hook...

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hat is the current the following circuit? 20.8 Series and Parallel Circuits Now let’s hook resistors up both in series and in parallel in the same circuit! What is the current I in the following circuit? We need to find the I I equivalent resistance! I I Thus, 40 , Ω 240 eq R V 24 I I eq R I A 1 . 0 240
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20.9 Internal Resistance So far we’ve just considered batteries and generators as contributing their emf to a circuit. In reality, they too have some resistance. This is called internal resistance, r . In batteries it’s due to the chemicals, and in generators it’s due to wire resistance. So, if a battery is connected to a load resistor, R , then the internal resistance, r , is in series with the load: Thus, the voltage across the ,g battery (known as the terminal voltage, V T ) is less than the full voltage V , since some is lost across r . otice: nd re in series! Thus, r T V V V = Notice: R and r are in series! V T Terminal voltage Battery voltage Voltage drop across the internal resistance, r
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Kirchhoff’s Rules In many circuits, applying the series or parallel methods is not sufficient to analyze them. There are two other rules we can use called Kirchhoff’s Rules : unction Rule urrent into a junction has to equal current out 1. Junction Rule Current into a junction has to equal current out. It is based on conservation of charge. I flows into junction, and I and I flow out, thus: 1 2 I 2 + I I 1 2 1 2. Loop Rule – Around any closed circuit loop, the sum of the potential (voltage) drops has to equal the sum of the potential rises. It is based on conservation of energy.
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Here’s an example with the loop rule. We have a closed circuit loop with multiple batteries. What is the current in the circuit?
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This note was uploaded on 04/24/2010 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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Lecture_9 - 20.8 Series and Parallel Circuits Now lets hook...

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