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What exactly is an ampere |
The flow of one coulomb per second |
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Just as water flows from a region of high pressure to a region of low pressure, electric charge flows from a region of |
high electric pressure to a region of low electric pressure |
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Voltage is most similar to |
pressure |
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The current produced by voltage in a circuit is impeded by |
electric resistance |
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Ohm’s law tells us that the amount of current produced in a circuit is |
directly proportional to voltage and inversely proportional to resistance |
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The resistance of a filament that carries 2 A when a 10-V potential difference across it is |
5 ohms |
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Direct current is normally produced by a |
battery |
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Alternating current is normally produced by a |
generator. |
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For electric current in the home, your power company supplies |
energy |
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The cause of electrical shock is predominantly |
excess voltage |
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One joule per coulomb is a unit of |
voltage |
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One kilowatt is a unit of |
power |
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One kilowatt-hour is a unit of |
energy |
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When a 12-V battery powers a single 6-ohm lamp |
12 joules flow in the lamp each second |
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By convention, the direction of current in a circuit is |
The direction in which positive charge flows and, from the positive terminal of a source to the negative terminal. |
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When two lamps are connected in series to a battery, the electrical resistance that the battery senses is |
More than the resistance of either lamp |
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When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is |
less than the resistance of either lamp. |
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When a pair of identical lamps are connected in parallel |
Voltage across each is the same Current in each is the same and Power dissipated in each is the same |
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Connect a pair of lamps in series and current is drawn from the battery. Connect the same lamps in parallel and the current drawn is |
more |
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The force that acts between a pair of magnetic poles depends on |
separation distance and magnetic pole strength |
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Whereas electric charges can be isolated, magnetic poles |
can not |
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Surrounding every magnet is |
a magnetic field |
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The conventional direction of magnetic field lines outside a magnet are from |
north to south |
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The end of a compass needle that points to the south pole of a magnet is the |
north pole |
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The lift experienced by Maglev trains is due to magnetic |
repulsion |
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When current reverses direction in a wire, the surrounding magnetic field |
also reverses direction |
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When a current-carrying wire is bent into a loop, its magnetic field inside the loop |
becomes concentrated |
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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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How much energy is supplied to each coulomb of charge that flows through a 12-V battery |
12 joules |
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Name two kinds of practical "electric pumps. |
Batteries and automobile alternators |
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What is the relationship between current, resistance, and voltage difference |
Current = Voltage Difference / Resistance |
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How does the current change if you increase the resistance, keeping the voltage difference the same |
The current decreases |
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What factors does the resistance offered by a piece of conductor depend upon |
both the geometry and the material of the conductor |
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How does the resistance of a thick piece of copper wire compare to the resistance of a thin piece of copper wire |
The resistance of the thin piece is greater than that of the thick piece |
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What is the current in a bulb if the resistance of its filament is 2 ohms and it is connected across a 6-volt battery |
3 amps |
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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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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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What does the power company provide to our homes |
It provides energy to move the electrons |
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Of what physical quantity is Hertz a unit of |
number of times per second that the electrons move back and forth in the wire |
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What type of field causes the electrons to do what they do in the wire |
electric field |
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What kind of current runs through the electric wiring in a home |
alternating current |
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Electrons flow in a wire when there is |
a potential difference across its ends |
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To think of electric potential difference we are thinking about |
voltage |
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The unit of electrical resistance is the |
ohm |
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Heat a copper wire and its electric resistance |
increases |
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Current in a conductor can be increased by |
reducing its resistance and increasing the voltage across it |
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The power consumed by a device drawing 0.8 A when connected to 120 V is |
96W |
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The brightness of a lamp is directly related to its |
power rating |
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What is the source of the magnetic force |
Electric charges in motion are the sources of magnetic forces |
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How is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles |
Like poles repel, unlike poles attract, and the force is proportional to the inverse square of the distance between two poles |
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In what way are magnetic poles very different from electric charges |
All magnets have both south and north poles. Electric charges can exist as singular entities. |
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Why will dropping an iron magnet on a concrete sidewalk make it a weaker magnet |
Vibrations provide energy to randomize the magnetic directions of the domains |
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Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire |
The magnetic field of each segment of wire in the loop, due to electrons moving in the wire, adds together inside the loop, thereby making the field become bunched-up |
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Like kinds of magnetic poles repel while unlike kinds of magnetic poles |
attract |
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In general, a common magnet has |
at least two poles |
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Magnetic domains normally occur in |
iron |
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Wood does not have magnetic properties because it contains no |
magnetic domains |
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Into which stable force field can a proton be placed at rest without being acted upon by a force |
magnetic field |
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Potential Difference |
The difference in electric potential between two points, measured in volts |
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Electric Current |
The flow of electric charge that transports energy from one place to another, measured in amperes, where 1 A is the flow of 6.25 * 10^18 electrons per second or 1 coulomb per second |
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Electrical Resistance |
The property of a material that resists electric current, measured in ohms |
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Ohm’s Law |
The statement that the current in a circuit varies in direct proportion to the potential difference or voltage across the circuit and inversely with the circuit’s resistance. Current = voltage/resistance A potential difference of 1 V across a resistance of 1 ohm produces a current of 1 A |
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Direct Current (dc) |
Electrically charged particles flowing in one direction only |
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Alternating Current (ac) |
Electrically charged particles that repeatedly reverse direction, vibrating about relatively fixed positions. In the United States, the vibrational rate is commonly 60hz |
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Electric Power |
The rate of energy transfer, or the rate doing work; the amount of energy per unit time, which can be computed as the product of current and voltage Power=current * voltage Electric power is measured in watts or kilowatts where 1 W= 1A * 1V= 1J/s |
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Series Circuit |
An electric circuit in which electrical devices are connected along a single loop of wire such that the same current is in each device |
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Parallel Circuit |
An electric circuit in which electrical devices are connected in such a way that the same voltage acts across each one, and any single one completes the circuit independently of all other |
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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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Electric power in a circuit is the rate at which |
energy dissipates |
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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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When your body undergoes electric shock, the source of moving electrons is |
electrons already in your body |
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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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A flow of electric charge in a wire normally requires a |
potential difference across the ends of the wire |
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The voltage across a 10-ohm resistor carrying 5 A is |
more than 20 V |
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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 the unit of electrical resistance |
Ohm |
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Using the formula power = current × voltage, find the current drawn by a 1000-W toaster connected to 140V |
W/V 1000W/140V |
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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 is the relationship among electric power, current, and voltage |
Power is current times voltage |
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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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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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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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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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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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A voltage source in a circuit provides electrical |
pressure |
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A 60-W light bulb connected to a 120-V source draws a current of |
W/V =I(A) 60W/120V = 0.5 I (A) |
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The entity that travels about the speed of light in an electric circuit is |
electric field |
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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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Two light bulbs are connected to a battery, one at a time. The bulb that draws more current has the |
lower resistance, and is brightest |
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What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed |
The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa |
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Magnetic field strength about a magnet is strongest where magnetic field lines are |
closer together |
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How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet |
the field strength is stronger where the field lines are closer |
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The fundamental rule for the attraction and repulsion of magnets is that |
like poles repel each other while opposite poles attract |
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Why is iron magnetic and wood not |
The magnetic fields of individual iron atoms are strong enough to align the magnetic fields of neighbor atoms. The atoms in wood have much weaker magnetic fields. |
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What is a magnetic domain |
Clusters of atoms with their magnetic fields aligned |
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An iron rod becomes magnetic when |
the net spins of many of its electrons are aligned |
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