Mastering Physics: Electric Current

A flow of electric charge in a wire normally requires a _________.

potential difference across the ends of the wire

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.

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

12 joules

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.

An electric current of 5 amperes in a wire carries _________.

5 joules per coulomb

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

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

A capacitor

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.

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.

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.

Name two kinds of practical "electric pumps."

Batteries and automobile alternators

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.

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.

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.

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

Energy

How does the heat emitted by lamps affect their efficiency?

Heat emitted reduces the efficiency.

Where do the electrons come from that produce an electric shock when you touch a charged conductor?

Inside you

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

It alternates back and forth 60 times a second.

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

It grounds the case to zero potential.

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.

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.

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.

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.

Why does a wire that carries electric current become hot?

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

What is the unit of electrical resistance?

Ohm

What is the relationship among electric power, current, and 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?

The battery is dc; the generator is ac.

What exactly is an ampere?

The flow of one coulomb per second

What is meant by drift velocity?

The net flow of electrons along a wire.

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.

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.

What is the function of fuse or circuit breaker in a circuit?

To prevent over loading the circuit with current

How does wetness affect the resistance of your body?

Wet bodies have lower resistance.

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

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

Wires are full of mobile electrons.

When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally _________.

continue glowing as brightly

The entity that travels about the speed of light in an electric circuit is _________.

electric field

When your body undergoes electric shock, the source of moving electrons is _________.

electrons already in your body

When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________.

go out

A voltage source in a circuit provides electrical _________.

pressure

The electric resistance in a length of wire is doubled when the wire is _________.

twice as long

Electrons in the filament of a lamp that carries ac have a net speed that is _________.

zero