Ch 23

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

Temperature difference is a necessary condition for the flow of heat. Similarly, a voltage difference is necessary for the flow of charge.

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

The water flow in the pipe occurs when a difference between water levels exists. The analogous situation is a difference in voltage inducing a flow if charge.

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

Protons cannot move because they are bound inside the nuclei of atoms, which are more or less locked in fixed positions. Electrons in metals are free to wander, which is why they are called charged carriers.

4. What exactly is an ampere?

One ampere is the electrical flow or current equal to one coulomb of charge per second.

5. Name two kinds of practical electric pumps.

Chemical batteries and electrical generators.

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

One volt means each Coulomb of charge can release one joule of energy. V= W/q. W= Vq E= Vq E= (1C)(12 V) = 12 J. Thus energy supplied to each coulomb if charge is 12 J.

7. Does charge flow through a circuit or into a circuit? Does voltage flow through a circuit or is voltage established across a circuit?

Charge flows through a circuit, and voltage is established across a circuit.

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?

Wide pipe and thick wire.

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

Increase electrical resistance.

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

Current will be halved.

11. 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?

Current will be halved.

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

Wetness decreases resistance of the body.

13. What is the function of the round third prong in a modern household electric plug?

The round third pong is connected to the body of the appliance, which is grounded. So if the live(hot) wire accidently comes in contact with the body if the appliance, you won’t receive the shock since the appliance casing is grounded by way of the round third prong.

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

The battery produces DC, and the generator at a power station produces AC.

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

This means that the current flows alternatively back and forth at a frequency of 60 Hz.

16. What property of a diode enables it to convert ac to pulsed dc?

A diode acts as a one-way valve that allows electrons to flow in only one direction.

17. A diode converts ac to dc. What electrical device smoothes the pulsed dc to a smoother dc?

A capacitor.

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

This is because it is not electrons that travel, it is the electric field that travels at about the speed of light.

19. Why does a wire that carries electric current becomes hot?

The electrons moving in the wire collide with metallic atoms in their path and transfer their kinetic energy to them. That is why current carrying wires become hot.

20. What is meant by drift velocity?

The net flow of electrons in a single direction in a conducting wire is called drift velocity.

21. A tipped domino sends a pulse along a row of standing dominoes. Is this a good analogy fir the way electricity, current, sound, or both travels?

This is a good analogy for sound, but not for electrical currents.

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

Electrons are already in the wire. The battery and generators are the only sources of energy.

23. When you make your household electric payment at the end of the month, which if the following are you billed for voltage, current, power, energy?

Energy

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

These electrons originate from the body.

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

Electric power= electric current x electric voltage.

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

The watt and kilowatt are units of energy, while a kilowatt-hour is a unit of power.

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

A 100 W lamp does not use all its energy to light a room but most of the amount is lost in the form of heat. So a 100 W lamp with 90% of its energy lost as heat is less efficient than a 25 W lamp with 10% of its energy lost as heat giving the same amount of light. Therefore, the efficiency of a lamp depends on the heat emitted.

28. 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.

The current through the other lamp is also 1 A. That’s because the electrical current has a single pathway through the circuit. This means the current passing through each bulb along the pathway is the same.

29. If a voltage of 6 V is impressed across the circuit in the preceding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp?

4V because the total voltage impressed across a series circuit is equal to the sim of the voltage drops across each individual bulb.

30. 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?

The same voltage, 6 volts.

31. How does the sum of the currents through the branches of a simple parallel circuit compare with the current that flows through the voltage source?

The sum of the currents through the branches of a simple parallel circuit is equal to the current that flows through the voltage source.

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

When the circuit is overloaded, the fuse blows and breaks the circuit. Thus, fuse or circuit breakers are used to protect lines.