Physics ch. 23

Find the cost in dollars of the operating a 60-W lamp continuously for 1 week when the power utility rate is 20 cents/kWh .

$2

Using the formula power = current × voltage, find the current drawn by a 900-W toaster connected to 80 V. Then, using the equation current = voltage/resistance, find the resistance of the toaster.

11.25 A 7.1 Ω

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 12 amps 0.33 amps

3 amps

An electric current of 5 amperes in a wire carries _________. 5 joules per ohm 5 coulombs per second 5 volts per coulomb 5 joules per coulomb 5 coulombs per joule

5 coulombs per second

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 flows across a circuit. Charge and voltage both flow across a circuit. Charge flows through and voltage is impressed across a circuit. Charge flows across and voltage is impressed across a circuit.

Charge flows through and voltage is impressed across a circuit

What is the relationship between current, resistance, and voltage difference? Current = Resistance / Voltage Difference Current = Voltage Difference x Resistance Current = Voltage Difference / Resistance

Current = Voltage Difference / Resistance

Why are electrons, rather than protons, the principal charge carriers in metal wires? Electrons are lighter, so they move faster than protons with the same kinetic energy. Protons are free to move through the metal, whereas electrons are fixed in place. Electrons are in the nucleus, whereas protons are in a cloud around the nucleus. Electrons are free to move through the metal, whereas protons are fixed in place.

Electrons are free to move through the metal, whereas protons are fixed in place.

When you make your household electric payment at the end of the month, are you billed for voltage, current, power, or energy? Voltage Power Energy Current

Energy

What is the function of the round third prong in a modern household electric plug? It provides safety against lightning strikes. It grounds the case to zero potential. It attaches the case to 120 volts potential. It supplies a backup source of voltage.

It grounds the case to zero potential.

Does heating a metal wire increase or decrease its electrical resistance? Why? It decreases resistance because atoms at higher temperatures jostle into the way of moving electrons. It decreases resistance because higher temperatures free more electrons to carry current. It increases resistance because atoms at higher temperatures jostle into the way of moving electrons. It decreases resistance because a metal becomes a superconductor when warmed.

It increases resistance because atoms at higher temperatures jostle into the way of moving electrons.

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 doubles. It stays the same. It quadruples. It is cut in half.

It is cut in half.

What does the power company provide to our homes? It provides neither electrons nor the energy to move the electrons. It provides electrons and the energy to move the electrons. It provides energy to move the electrons. It provides electrons that travel through the wire.

It provides energy to move the electrons.

Why does a wire that carries electric current become hot? Moving electrons collide with atoms, which transfers their kinetic energy to atomic motion. The electric field producing the current pushes on the atoms, which makes them move. Electrons collide with other electrons and the collisions produce sparks that heat the wire. Every time an electron changes direction in an ac circuit, it pushes on nearby atoms, which makes them move. Dc current does not heat the wire.

Moving electrons collide with atoms, which transfers their kinetic energy to atomic motion

What is the unit of electrical resistance? Volt Amp per volt Amp Ohm

Ohm

What is the relationship among electric power, current, and voltage? Power is voltage divided by current. Power is current divided by voltage. Power is current times voltage. Power is voltage.

Power is current times voltage.

Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac? Both are ac. Both are dc. The battery is ac; the generator is dc. The battery is dc; the generator is ac.

The battery is dc; the generator is ac.

How does the current change if you increase the resistance, keeping the voltage difference the same? The current increases. The current decreases. The current stays the same.

The current decreases

What is the effect on the current in a wire if both the voltage across it and its resistance are doubled? The current is doubled. The current is halved. The current remains unchanged. If both are halved? The current is halved. The current is doubled. The current remains unchanged.

The current remains unchanged. The current remains unchanged.

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 thick piece is greater than that of the thin piece. The resistance of the thin piece is greater than that of the thick piece. Both the wire and narrow piece of copper provide the same resistance.

The resistance of the thin piece is greater than that of the thick piece.

What kind of current runs through the electric wiring in a home? circular current alternating current direct current

alternating current

What factors does the resistance offered by a piece of conductor depend upon? only the geometry of the conductor both the geometry and the material of the conductor material of the conductor neither the geometry nor the material of the conductor

both the geometry and the material of the conductor

When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally _________. continue glowing as brightly absorb energy from the damaged lamp go out continue glowing, but dimme

continue glowing as brightly

Two lightbulbs are hooked up to a battery in parallel. If one of the lightbulbs is disconnected, the other lightbulb will __________. get brighter continue shining with the same brightness stop shining get dimmer

continue shining with the same brightness

The entity that travels about the speed of light in an electric circuit is _________. electric field voltage and electric field, but not current voltage current

electric field

What type of field causes the electrons to do what they do in the wire? magnetic field electric field electric and magnetic fields.

electric field

What type of particle is responsible for a current flowing through a metallic wire? electron neutrons protons neutrinos

electron In a conductor, an electric field causes the outer electrons of each atom to be ripped off and drift through the wire; the resulting current is in the opposite direction since the electrons are negatively charged.

When your body undergoes electric shock, the source of moving electrons is _________. moisture between you and a voltage source the object making electrical contact electrons already in your body mainly from the ground

electrons already in your body

Electric power in a circuit is the rate at which _________. voltage dissipates energy dissipates current dissipates wattage dissipates

energy dissipates

Two lightbulbs are connected in series to a battery, as shown in the figure. The magnitude of the current flowing through bulb #2 is ___________. equal to that flowing through bulb #1 twice that flowing through bulb #1 half that flowing through bulb #1

equal to that flowing through bulb #1

When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________. continue glowing, but dimmer absorb energy from the damaged lamp go out continue glowing as brightly

go out

A battery is hooked up to a lightbulb, as shown in the figure. If the voltage difference of the battery were doubled, the resulting current flowing through the lightbulb would ________. increase by a factor of 2 decrease by a factor of 2 increase by a factor of 4 remain the same

increase by a factor of 2 As described by Ohm's law, V=IR, the current is proportional to the voltage if the resistance is constant.

A battery is hooked up to a lightbulb, as shown in the figure. If the voltage difference of the battery were doubled, the resulting electric power would ______. remain the same increase by a factor of 2 decrease by a factor of 2 increase by a factor of 4

increase by a factor of 4 Since P=VI, and since the current doubles when the voltage doubles, the power increases by a factor of 4.

Of what physical quantity is Hertz a unit of? number of times per second that the electrons move back and forth in the wire speed at which the electrons travel down the wire time taken by electrons as they travel down the wire

number of times per second that the electrons move back and forth in the wire

A flow of electric charge in a wire normally requires a _________. sustained energy difference across the ends of the wire potential difference across the ends of the wire voltage source pump

potential difference across the ends of the wire

A voltage source in a circuit provides electrical _________. resistance pressure force grounding

pressure

A lightbulb is labeled "100 watts." What does "100 Watts" represent? the voltage of the battery the bulb should be attached to the current flowing through the filament when the bulb is on the resistance of the filament the rate of energy being dissipated within the filament of the bulb when the bulb is on

the rate of energy being dissipated within the filament of the bulb when the bulb is on The measurement 100 watts means that when a lightbulb is plugged into a standard U.S. outlet, 100 joules of electrical energy is converted into heat every second.

The electric resistance in a length of wire is doubled when the wire is _________. properly insulated twice as long doubled in temperature half as long

twice as long

In one circuit, identical lightbulbs are hooked up to a 20-volt battery, as shown in the figure. In the other circuit, a third identical lightbulb is attached to another 20-volt battery. The current flowing through the circuit containing two lightbulbs is _________. four times lower than that flowing through the circuit containing one lightbulb two times lower than that flowing through the circuit containing one lightbulb the same as that flowing through the circuit containing one lightbulb

two times lower than that flowing through the circuit containing one lightbulb The resistance of two identical resistors in series is twice the resistance of one resistor. Since the current is proportional to the inverse of the resistance, the current is half as much as the circuit with one resistor.

Electrons in the filament of a lamp that carries ac have a net speed that is _________. about the speed of sound about the speed of light zero very low, about a snail's pace

zero