Physics 100-Chapter 23-Reading Check Questions

25. In a circuit of two lamps in series, if the current through one lamp is 1 A, what is the current through the other lamp? Defend your answer.

-1 amp -the same current flows through lamps in series

32. Current

-I -flow of electrons measured in coulombs/second -flow of electric charge

5. Name two kinds of practical "electrical pumps."

-generators and chemical batteries

19. What is the error in saying that the source of electrons in a circuit is the battery or generator?

-wires are full of mobile electrons

6. How much energy is supplied to each coulomb of charge that flows through a 12-V battery?

-12 J of energy

26. If a voltage of 6 V is impressed across the circuit in the receding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp? Defend your answer.

-4 volts -the sum of the voltages across each lamp must add up to the total voltage across both lamps

29. In a circuit of two lamps in parallel, if there is a voltage of 6 V across one lamp, what is the voltage across the other lamp?

-6 volts

24. How does the heat emitted by lamps affect their efficiency?

-90% of the energy transferred by an incandescent bulb is heat

34. Voltage

-V (volts) -work/energy term related to force; w = Fd -joule/coulomb EX: 6 V battery = 6 j/coulomb -provides electrical pressure to move electrons through a circuit

15. Does a battery produce dc or ac? Does the generator at a power station produce dc or ac?

-a battery produces dc -a generator produces ac

2. What condition is necessary for the sustained flow of water in a pipe? What analogous condition is necessary for the sustained flow of charge in a wire?

-a continuous pressure difference, often provided by a pump -a continuous potential difference -(the flow of water from a higher reservoir to a lower one)

8. Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire?

-a wide pipe -thick wire

33. Coulombs/sec

-ampere -1 amp is same as 1 coulomb/sec -rate of electrical charge

17. What is meant by drift velocity?

-average velocity of electrons moving in a wire

3. Why are electrons, rather than protons, the principal charge carriers in metal wires?

-because one or more electrons from each metal atom are free to move throughout the atomic lattice

7. Does electric charge flow across a circuit or through a circuit? Does voltage flow across a circuit or is it impressed across a circuit?

-electric charge flows through a circuit because of an applied voltage across the circuit -voltage is impressed across a circuit

20. When you make your household electric payment at the end of the month, which are you billed for: voltage, current, power or energy?

-energy

11. If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?

-if the resistance is doubled, the current is halved (the current in a circuit is directly proportional to the voltage established across the circuit and is inversely proportional to the resistance of the circuit)

9. Does heating a metal wire increase or decrease its electrical resistance?

-increases the resistance

21. From where do the electrons originate that produce an electric shock when you touch a charged conductor?

-inside your body

14. What is the function of the round third prong in a modern household electrical plug?

-it connects directly to the ground

15. What is the error in saying that electrons in a common battery-driven circuit travel at about the speed of light?

-it is the electric field that can travel through a circuit at nearly the speed of light; electrons are moving in all possible directions so they do not move at almost the speed of light

13. How does wetness affect the resistance of your body?

-lowers your skin resistance to a few hundred ohms or less (depending on the distance over which the voltage acts)

35. Ohms

-measurement of electrical resistance -Ohm's Law Current = voltage over resistance Amperes = volts over ohms (units of measurement)

16. Why does a wire that carries electric current become hot?

-moving electrons collide with atoms, which transfers their kinetic energy to atomic motion.

18. A tipped domino sends a pulse along a row of standing dominoes. Is this a good analogy for the way electric current, sound, or both travel?

-no -it is a good analogy for the transmission of sound but not for the transmission of electric energy

10. What is the unit of electrical resistance?

-ohms

22. What is the relationship among electric power, current and voltage?

-power = current X voltage (in units: Watts = amperes X volts)

1. What condition is necessary for the flow of heat? What analogous condition is necessary for the flow of charge?

-temperature difference (flows from high temperature to low temperature) -a difference in electrical potential (potential difference) is needed for charge to flow

12. If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current?

-the less the voltage the less the current, so the current will end up being half its former value

4. What exactly is an ampere?

-the rate of electrical flow (1 coulomb of charge per second)

30. How does the sum of the currents through the branches of a simple parallel circuit compare with the current in the voltage source?

-the sum of the currents in the branches equals the current through the source

31. What is the function of fuses or circuit breakers in a circuit?

-to prevent over loading the circuit with current

16. What does it mean to say that a certain current is 60 Hz?

-voltages and currents that alternate back and forth at a frequency of 60 cycles per second

23. Which of these is a unit of power and which is a unit of energy: a watt, a kilowatt, a kilowatt-hour?

-watt = power -kilowatt = power -kilowatt-hour = energy