Lecture%2021C

# Lecture%2021C - Physics 1B Lecture 21C Circuits Lets say we...

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Physics 1B Lecture 21C

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Circuits Let’s say we have a circuit with two resistors in parallel. When these two resistors are hooked up to the battery, a current is established. In this circuit, both resistors would have the same potential difference as the battery. ΔV bat = ΔV 1 = ΔV 2
We can essentially replace the two resistors in parallel with one equivalent resistor. As the current, I, approaches point a (a junction), it will break up into I 1 and I 2 . I = I 1 + I 2 R eq The battery sees current I passing through it and believes that the one equivalent resistor has a potential difference of ΔV bat .

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Circuits In general, for parallel resistors: So, to the battery the equivalent resistance is: R eq
Question The equivalent resistance for a group of resistors in parallel is: A) less than any resistor in the group. B) equal to the smallest resistance in the group. C) equal to the average resistance of the group. D) equal to the largest resistance in the group. E) larger than any resistor in the group. n eq R R < n eq R R 1 1 >

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Circuits Example What is the current (I) that leaves the battery in the following circuit? Answer Reduce the circuit by equivalent resistance and then use Ohm’s Law to solve for the current.
Circuits All three resistors are in parallel, so we can use: Answer

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Circuits We can write the equivalent circuit and apply Ohm’s Law: Answer
Circuits Example What is the current (I) that flows through the battery? Answer Reduce the circuit by equivalent resistance and then use Ohm’s Law to solve for the current. First, take the two pairs of resistors that are in parallel and find their equivalent resistance.

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Circuits Start with the two resistors in the top right corner: Answer Then, for the two resistors in the lower left corner:
Next, combine the two pairs f resistors that are in series: Answer Next, combine the pair of esistors that are in parallel:

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Finally, combine the pair of resistors that are in series: Answer We can apply Ohm’s Law for this equivalent circuit:
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## This note was uploaded on 01/30/2012 for the course PHYSICS 1B 1B taught by Professor Grosmain during the Winter '10 term at UCSD.

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Lecture%2021C - Physics 1B Lecture 21C Circuits Lets say we...

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