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Unformatted text preview: Physics for Scientists and Engineers, 6e Chapter 28 – Direct Current Circuits In order to maximize the percentage of the power that is delivered from a battery to a device, the internal resistance of the battery should be 1 2 3 33% 33% 33% 1 2 3 4 5 1. as low as possible 2. as high as possible 3. The percentage does not depend on the internal resistance. Power is delivered to the internal resistance of a battery, so decreasing the internal resistance will decrease this “lost” power and increase the percentage of the power delivered to the device. In the figure below, imagine positive charges pass first through R 1 and then through R 2 . Compared to the current in R 1 , the current in R 2 is 1 2 3 4 5 1. smaller 2. larger 3. the same 1 2 3 33% 33% 33% In a series circuit, the current is the same in all resistors in series. Current is not “used up” as charges pass through a resistor. If a piece of wire is used to connect points b and c in Figure 28.4b, the brightness of bulb R 1 will 1 2 3 33% 33% 33% 1 2 3 4 5 1. increase 2. decrease 3. remain the same Connecting b to c “shorts out” bulb R 2 and changes the total resistance of the circuit from R 1 + R 2 to just R 1 . Because the resistance of the circuit has decreased (and the emf supplied by the battery does not change), the current in the circuit increases. With the switch in this circuit closed (left), there is no current in R 2 , because the current has an alternate zeroresistance path through the...
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This note was uploaded on 01/19/2010 for the course PHYS 200 taught by Professor Davies during the Spring '08 term at Roger Williams.
 Spring '08
 Davies
 Current, Resistance, Power

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