CHAPTER 23 Flashcards
A flow of electric charge in a wire normally
requires a _________.
potential difference across the ends of
the wire
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.
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.
What exactly is an ampere?
The flow of one coulomb per second
A voltage source in a circuit provides electrical
_________.
pressure
The work done to separate opposite charges
results in different values of energy per
charge. What is this difference called?
Potential difference or voltage
How much energy is supplied to each coulomb
of charge that flows through a 12-V battery?
12 joules
The electric resistance in a length of wire is
doubled when the wire is _________.
twice as long
Superconductors have near zero electrical resistance; how is this condition reached?
Expose the conductor to very low temperatures.
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
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 is the relationship between current, resistance, and voltage difference?
Current = Voltage Difference / Resistance
How does the current change if you increase
the resistance, keeping the voltage difference
the same?
The current decreases.
What factors does the resistance offered by a
piece of conductor depend upon?
both the geometry and the material of
the conductor
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.
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
Which of the following would double the
amount of current flowing through a piece of
metal wire?
Double the voltage across it.
If the resistivity of copper is less than that of
gold at room temperature, which of the following statements must be true?
Electrons in gold are more likely to be
scattered than electrons in copper at
room temperature when they are accelerated by the same electric field.
How do the resistances of two conducting
wires compare if they have the same length,
but one is twice the radius of the other?
The thicker wire has one-fourth the resistance of the thinner wire.
Rank the wires in order of which carries the
most current (has the lowest resistance) when
connected to batteries with the same voltage
difference.
Most:
1. Wire of length L and area 2A
Middle:
2. Wire of length L and area A
Least:
3. Wire of length 2L and area A
What happens to the current in a circuit where
the resistance is kept constant and the voltage
is double?
Current also doubles.
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.
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.
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.
