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Chapter 23: Electric Current

6) Your friend says that a battery supplies the electrons in an electric circuit. Do you agree or disagree? Defend your answer.

12) Suppose you leave your car lights on while at a movie. When you return, your battery is too “weak” to start your car. A friend comes and gives you a jump start with his battery and battery cables. What physics is occurring here?

15) Why is the current in an incandescent bulb greater immediately after it is turned on than it is a few moments later? (That’s why bulbs usually burn out just as they are being turned on.)

18) A simple lie detector consists of an electric circuit, one part of which is part of your body—like from one finger to another. A sensitive meter shows the current that flows when a small voltage is applied. How does this technique indicate that a person is lying? (And when does this technique not tell when someone is lying?)

24) If a current of one- or two-tenths of an ampere flows into one of your hands and out the other, you will probably be electrocuted. But if the same current flows into your hand and out the elbow above the same hand, you can survive even though the current may be large enough to burn your flesh. Explain.

26) Are automobile headlights wired in parallel or in series? What is your evidence?

46) In the circuit shown, how do the brightnesses of the identical light bulbs compare? Which bulb draws the most current? What will happen if bulb A is unscrewed? If C is unscrewed?

47) As more and more bulbs are connected in series to a flashlight battery, what happens to the brightness of each bulb? Assuming heating inside the battery is negligible, what happens to the brightness of each bulb when more and more bulbs are connected in parallel?

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