Physics Chapter 23 – Flashcards
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What condition is necessary for the flow of heat? What analogous condition is necessary for the flow of charge?
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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?
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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.
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Why are electrons, rather than protons, the principal charge carriers in metal wires?
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Electrons are free to move through the metal, whereas protons are fixed in place
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What exactly is an ampere?
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The flow of one coulomb per second
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Name two kinds of practical "electric pumps."
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Batteries and automobile alternators
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How much energy is supplied to each coulomb of charge that flows through a 12-V battery?
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12 joules
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Does electron charge flow across a circuit or through a circuit? Does voltage flow across a circuit or is it impressed across a circuit?
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Charge flows through and voltage is impressed a circuit
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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?
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Wide pipe and thick wire
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Does heating a metal wire increase or decrease its electrical resistance? Why?
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It increases resistance because atoms at higher temperatures jostle into the way of moving electrons
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What is the unit of electrical resistance?
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Ohm
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If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?
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It is cut in half
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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?
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It is cut in half
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How does wetness affect the resistance of your body?
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Wet bodies have lower resistance
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What is the function of the round third prong in a modern household electric plug?
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It grounds the case to zero potential
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Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac?
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The battery is dc; the generator is ac.
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What does it mean to say that a certain current is 60 Hz?
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It alternates back and forth 60 times a second
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What property of a diode enables it to convert ac to pulsed dc?
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It is a one-way valve that allows electrons to in one direction only
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A diode converts ac to pulsed dc. What electrical device smooths the pulsed dc to a smoother dc/
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A capacitor
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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?
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Electrons move at 0.01 cm/s. The electric field propagates at nearly the speed of light/
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Why does a wire that carries electric current become hot?
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Moving electrons collide with atoms, which transfer their kinetic energy to atomic motion
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What is meant by drift velocity?
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The net flow of electrons along a wire.
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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?
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This is the way sound travels but not how electric current travels.
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When you make your household electric payment at the end of the month, are you billed for voltage, current, power, or energy?
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Energy
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What is the error in saying the source of electrons in a circuit is he battery or generator?
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Wire are full of mobile electrons
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Where do the electrons come from that produce an electric shock when you touch a charged conductor?
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Inside you
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between a watt, a kilowatt, and a kilowatt-hour, which is a unit of power and which is a unit of energy?
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A watt is power, a kilowatt is power, and a kilowatt-hour is energy.
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How does the heat emitted by lamps affect their efficiency?
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Heat emitted reduces the efficiency.
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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
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1 amp. The same current flows through lamps in series
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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.
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4 volts. The sum of the voltages across each lamp must add up to the total voltage across both lamps
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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?
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6 volts
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How do the currents through the branches of a simple parallel circuit compare with the current in the voltage source?
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The sum of the currents in the branches equals the current through the source
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What is the function of fuse or circuit breaker in a circuit?
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To prevent over loading the circuit with current/
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A flow of electric charge in a wire normally requires a _________.
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Potential difference across the ends of the wire
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An electric current of 5 amperes in a wire carries _________.
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5 coulombs per second
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A voltage source in a circuit provides electrical _________.
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pressure
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The electric resistance in a length of wire is doubled when the wire is__________.
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twice as long
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When your body undergoes electric shock, the source of moving electrons is __________.
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electrons already in your body
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Electrons in the filament of a lamp that carries ac have a net speed that is_________.
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zero
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The entity that travels about the speed of light in an electric circuit is __________
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electric field
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What is the relationship among electric power, current, and voltage?
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Power is current times voltage.
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Electric power in a circuit is the rate at which___________.
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energy dissipates
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When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________.
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go out
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When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally_________.
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continue glowing as brightly
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What is the effect on the current in a wire if both the voltage across it and its resistance are doubles?
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The current remains unchanged
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If both are halved?
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The current remains unchanged
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Electric charge flows from a region _______ electric potential to an area of _______ electric potential.
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high; low
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Suitable electric pumps for electric circuits are ________ and _________
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generators; batteries
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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.
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voltage
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If we think about potential difference we are thinking about __________
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voltage
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The unit for current is the _________
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ampere
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When contemplating voltage, current and resistance, pressure is most similar to _________
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voltage
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Charge flows ___ a circuit, while voltage flows ________ it
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in; across
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The ohm is the unit for electrical ___________
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resistance
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The role of ________ is to impede current in a circuit
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resistance
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If two copper wires of the same length have different thickness, then the thicker wire has ______ resistance
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less
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As the temperature of a wire increases, its electrical resistance ____________
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also increases
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Thinner wires have ______ resistance than thicker ones
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more
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Light bulbs with more resistance have ________ light bulbs while bulbs with less resistance have ________ light bulbs
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dimmer; brighter
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Name two ways current in a wire can be increased.
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By increasing the voltage across it and by reducing its resistance
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Direct current is normally produced by a ________ while a generator could produce ______________
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battery; alternating current
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How is a capacitor useful?
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It is useful in smoothing pulsed currents
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What are electric diodes used for?
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They are used to change ac to dc
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Do electric companies supply electrons? If not, then what do they supply?
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No, they supply energy
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Electrons used in electric circuits are stored in _________________
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the circuits themselves
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The source of energy that powers a hair dryer is _______________
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the power company
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In order for electrons to flow in an electrical circuit they must interact with _____________________
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an established electric field
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The electric field in dc current established by a battery acts in _________
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one direction
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The electric field in ac current established by a generator acts in ____________
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two directions
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How is power defined?
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Energy expended/time
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Power = ___________
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current x voltage
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1 watt = 1 ____________
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amperes x volts
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1 volt = 1 ______________
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Joule/coulomb
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A unit of power is a ___________-
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kilowatt
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One kilowatt-hour is a unit of _______
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energy
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The power rating on a lamp will be directly related to its __________
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brightness
