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What exactly is an ampere? |
The flow of one coulomb per second |
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Why are electrons, rather than protons, the principal charge carriers in metal wires? |
Electrons are free to move through the metal, whereas protons are fixed in place. |
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What condition is necessary for the flow of heat? What analogous condition is necessary for the flow of charge? |
A difference in temperature is needed for heat to flow. A difference in electrical potential is needed for charge to flow. |
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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, is needed for water to flow. A continuous potential difference, often provided by a battery, is needed for charge to flow. |
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A flow of electric charge in a wire normally requires a _________. |
potential difference across the ends of the wire |
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Name two kinds of practical "electric pumps." |
Batteries and automobile alternators |
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How much energy is supplied to each coulomb of charge that flows through a 12-V battery? |
12 joules |
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Does electric charge flow across a circuit or through a circuit? Does voltage flow across a circuit or is it impressed across a circuit? |
Charge flows through and voltage is impressed across a circuit. |
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An electric current of 5 amperes in a wire carries _________. |
5 joules per coulomb |
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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 |
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Does heating a metal wire increase or decrease its electrical resistance? Why? |
It increases resistance because atoms at higher temperatures jostle into the way of moving electrons. |
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What is the unit of electrical resistance? |
Ohm |
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A voltage source in a circuit provides electrical _________. |
pressure |
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If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current? |
It is cut in half. |
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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? |
It is cut in half. |
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How does wetness affect the resistance of your body? |
Wet bodies have lower resistance. |
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What is the function of the round third prong in a modern household electric plug? |
It grounds the case to zero potential. |
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The electric resistance in a length of wire is doubled when the wire is _________. |
twice as long |
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Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac? |
The battery is dc; the generator is ac. |
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What does it mean to say that a certain current is 60 Hz? |
It alternates back and forth 60 times a second. |
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What property of a diode enables it to convert ac to pulsed dc? |
It is a one-way valve that allows electrons to in one direction only. |
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A diode converts ac to pulsed dc. What electrical device smoothes the pulsed dc to a smoother dc? |
A capacitor |
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When your body undergoes electric shock, the source of moving electrons is _________. |
electrons already in your body |
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At what speed do electrons in a battery driven automotive circuit travel along a wire? At what speed does the electric field propagate along a wire? |
Electrons move at 0.01 cm/s. The electric field propagates at nearly the speed of light. |
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Why does a wire that carries electric current become hot? |
Moving electrons collide with atoms, which transfers their kinetic energy to atomic motion. |
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What is meant by drift velocity? |
The net flow of electrons along a wire. |
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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? |
This is the way sound travels but not how electric current travels. |
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What is the error in saying the source of electrons in a circuit is the battery or generator? |
Wires are full of mobile electrons. |
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When you make your household electric payment at the end of the month, are you billed for voltage, current, power, or energy? |
Energy |
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Where do the electrons come from that produce an electric shock when you touch a charged conductor? |
Inside you |
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Electrons in the filament of a lamp that carries ac have a net speed that is _________. |
zero |
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What is the relationship among electric power, current, and voltage? |
Power is current times voltage. |
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Between a watt, a kilowatt, and a kilowatt-hour, which is a unit of power and which is a unit of energy? |
A watt is power, a kilowatt is power, and a kilowatt-hour is energy. |
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The entity that travels about the speed of light in an electric circuit is _________. |
electric field |
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How does the heat emitted by lamps affect their efficiency? |
Heat emitted reduces the efficiency. |
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In a circuit of two lamps in series, where 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. |
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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? Defend your answer. |
4 volts. The sum of the voltages across each lamp must add up to the total voltage across both lamps. |
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In a circuit of two lamps in parallel, where there is a voltage of 6 V across one lamp, what is the voltage across the other lamp? |
6 volts |
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How do 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. |
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What is the function of fuse or circuit breaker in a circuit? |
To prevent over loading the circuit with current |
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When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________. |
go out |
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When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally _________. |
continue glowing as brightly |
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