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QuestionsCh26 - CHAPTER 26 DC Circuits Responses to...

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CHAPTER 26: DC Circuits Responses to Questions 1. Even though the bird’s feet are at high potential with respect to the ground, there is very little potential difference between them, because they are close together on the wire. The resistance of the bird is much greater than the resistance of the wire between the bird’s feet. These two resistances are in parallel, so very little current will pass through the bird as it perches on the wire. When you put a metal ladder up against a power line, you provide a direct connection between the high potential line and ground. The ladder will have a large potential difference between its top and bottom. A person standing on the ladder will also have a large potential difference between his or her hands and feet. Even if the person’s resistance is large, the potential difference will be great enough to produce a current through the person’s body large enough to cause substantial damage or death. 2. Series: The main disadvantage of Christmas tree lights connected in series is that when one bulb burns out, a gap is created in the circuit and none of the bulbs remains lit. Finding the burned-out bulb requires replacing each individual bulb one at a time until the string of bulbs comes back on. As an advantage, the bulbs are slightly easier to wire in series. Parallel: The main advantage of connecting the bulbs in parallel is that one burned-out bulb does not affect the rest of the strand, and is easy to identify and replace. As a disadvantage, wiring the bulbs in parallel is slightly more difficult. 3. Yes. You can put 20 of the 6-V lights in series, or you can put several of the 6-V lights in series with a large resistance. 4. When the bulbs are connected in series, they have the same current through them. R 2 , the bulb with the greater resistance, will be brighter in this case, since P = I ² R . When the bulbs are connected in parallel, they will have the same voltage across them. In this case, R 1 , the bulb with the lower resistance, will have a larger current flowing through it and will be brighter: P = V ² /R . 5. Double outlets are connected in parallel, since each has 120 V across its terminals and they can be used independently. 6. Arrange the two batteries in series with each other and the two bulbs in parallel across the combined voltage of the batteries. This configuration maximizes the voltage gain and minimizes the equivalent resistance, yielding the maximum power.
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