Physics Chapter 23
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.
How is power defined?
Energy expended/time
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
How is a capacitor useful?
It is useful in smoothing pulsed currents
One kilowatt-hour is a unit of _______
energy
If we think about potential difference we are thinking about __________
voltage
In order to keep artificial waterfalls going a pump is needed to pump the water back to the top of the falls. In the same way, in electric circuit the flow of charge needs ________ to keep the charges flowing.
voltage
When contemplating voltage, current and resistance, pressure is most similar to _________
voltage
Electrons in the filament of a lamp that carries ac have a net speed that is_________.
zero
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 coulombs per second
In a circuit of two lamps in parallel, where there is a voltage of V across one lamp, what is the voltage across the other lamp?
6 volts
A diode converts ac to pulsed dc. What electrical device smooths 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 different, 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.
Name two kinds of practical "electric pumps."
Batteries and automobile alternators
Name two ways current in a wire can be increased.
By increasing the voltage across it and by reducing its resistance
Does electron 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 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
1 volt = 1 ______________
Joule/coulomb
Why does a wire that carries electric current become hot?
Moving electrons collide with atoms, which transfer their kinetic energy to atomic motion
Do electric companies supply electrons? If not, then what do they supply?
No, they supply energy
What is the unit of electrical resistance?
Ohm
A flow of electric charge in a wire normally requires a _________.
Potential difference across the ends of the wire
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.
If both are halved?
The current remains unchanged
What is the effect on the current in a wire if both the voltage across it and its resistance are doubles?
The current remains unchanged
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
What are electric diodes used for?
They are used to change ac to dc
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 he battery or generator?
Wire are full of mobile electrons
As the temperature of a wire increases, its electrical resistance ____________
also increases
The unit for current is the _________
ampere
1 watt = 1 ____________
amperes x volts
In order for electrons to flow in an electrical circuit they must interact with _____________________
an established electric field
Direct current is normally produced by a ________ while a generator could produce ______________
battery; alternating current
The power rating on a lamp will be directly related to its __________
brightness
When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally_________.
continue glowing as brightly
Power = ___________
current x voltage
Light bulbs with more resistance have ________ light bulbs while bulbs with less resistance have ________ light bulbs
dimmer; brighter
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
Electric power in a circuit is the rate at which___________.
energy dissipates
Suitable electric pumps for electric circuits are ________ and _________
generators; batteries
When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________.
go out
Electric charge flows from a region _______ electric potential to an area of _______ electric potential.
high; low
Charge flows ___ a circuit, while voltage flows ________ it
in; across
A unit of power is a ___________-
kilowatt
If two copper wires of the same length have different thickness, then the thicker wire has ______ resistance
less
Thinner wires have ______ resistance than thicker ones
more
The electric field in dc current established by a battery acts in _________
one direction
A voltage source in a circuit provides electrical _________.
pressure
The ohm is the unit for electrical ___________
resistance
The role of ________ is to impede current in a circuit
resistance
Electrons used in electric circuits are stored in _________________
the circuits themselves
The source of energy that powers a hair dryer is _______________
the power company
The electric resistance in a length of wire is doubled when the wire is__________.
twice as long
The electric field in ac current established by a generator acts in ____________
two directions
