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36 Cards in this Set
- Front
- Back
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Why are electrons, rather than protons, the principal charge carriers in metal wires?
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Because one or more electrons from each metal atom are free to move throught the atomic lattice. While protons do not move because they are bound inside the nuclei of atoms
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What exactly is an ampere?
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it is what electrical flow is measured in, one ampere is a flow equal to 1 coulomb of charge per second.
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Why is a current-carrying wire normally not electrically charged?
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There are as many electrons as protons in the wire.
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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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A wide pipe. Likewise a thick wire conducts more electricity.
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Does heating a copper wire increase or decrease its electrical resistance?
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Increased temperature means increased resistance
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How does a superconductor differ from an ordinary conductor?
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The superconducter needs much lower temperatures for there to be zero resistance than regular conductors
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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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current is directly proportional to the voltage established across the circuit, and is inversely proportional to the resistance of the circuit. So if the resistance is double the current is halfed...
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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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The less the voltage the less the current, so the current will end up being half its former value
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What role do resistors normally play in an electric circuit?
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They are used to regulate the current.
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How does wetness affect the resistance of your body?
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It decreases the resistance of your body.
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What happens to the resistance of your skin when you perspire?
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the salf left from perspiration when wet lowers your skin resistance to a few hundred ohms or less.
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Why is it a very poor idea to handle electrical devices while i the bathtub?
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Because your overall resistance between you and the pipes in the bathtube that connect you to the ground is so low that the 120 volt potential difference will produce a harmful current in your body
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High voltage by itself does not produce electric shock. What does?
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The difference in elecrtical potential between one part of your body and another part when touching a current, it will pass along the path of least electrical resistance between two points.
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What is the function of the third prong in a modem household electric plug?
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The third prong is connected directly to th earth so it serves as a grounding device in the e event the live wirey comes in contact with the metal surface of the appliance.
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Distinguish between dc and ac.
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Dc means direct current and refers to the flowing of charges in one direction. A batteris terminals always ahve the same sign adn is Dc because the current runs in the same direction. Alternating Current move first in one direction then move in the opposite direction.
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Does a battery produce dc or ac? Does the generator at a power station produce dc or ac?
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a battery is Dc, While 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 means the voltages and currents alternate back and forth at a frequency of 60 cycles per second.
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What property of a diode enables it to convert ac to pusled dc?
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it is a tiny electronic device that acts as a one-way valve to allow electron flow in only one direction.
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A diode converts ac to pulsed dc. What electrical device smoothes the pulsed dc to a smoother dc?
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A capacitor
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What is the relationship among electric power, current, and voltage?
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electric power is equal to the product of current and voltage. , if the voltage is expressed in volts and the current in amperes, then the power is expressed in watts, so in units form, Watts= amperes X volts
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Which of these is a unit of power and which is a unit of energy: a watt; a kilowatt; a kilowatt-hour?
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a watt: power
a kilowatt: 1000 watts a kilowatt-hour: represents the amoung of energy consumed in 1 hour at the rate of 1 kilowatt |
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Distinguish between a kilowatt and a kilowatt-hour.
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a kilowatt is 1000 watts while a kilowatt-hour represents the amount of energy consumed in 1 hour at the rate of 1 kilowatt.
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What is an electric circuit?
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a path along whcih electrons flow
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In a circuit of two lamps in series, if the current through one lamp is 1 A, what is the current through the other lamp?
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1A
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If 6 V are impressed across the above circuit and the voltage across the first lamp is 2 V, what is the voltage across the second lamp?
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4v
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What is a main shortcoming of a series circuit?
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If one lamp blows out the whole circuit stops functioning
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In a circuit of two lamps in parallel, if there are 6 V across one lamp, what is the voltage across the other lamp?
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6V
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If the current through each of the two branches of a parallel circuit is the same, what does this tell you about the resistance of the two branches?
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the amount of current in each branch is inversely proportional to the resistance of the branch - Ohm's law applies separately to each branch.
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How does the total current through the branches of a simple parallel circuit compare to the current that flows through the voltage source?
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since the voltage across each branch is the same, the amount of current in each branch is inversely proportional to the resistance of the branch, ohm's law applies separately to each branch.
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As more lines are added at a fast food restaurant, the resistance to getting people served is reduced. How is this similar to what happens when more branches are added to a parallel circuit?
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Because the overall resistance of the circuit is less than the resitance of any one of the branches.
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Are household circuits normally wired in a series or in parallel?
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Parallel
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How does the amount of current in a home circuit differ from the amount of current in a reading lamp?
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a lamp draws around 2 amperes while the home lines have about 1110-120volts
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Why will too many electrical devices operating at one tie often blow a fuse or trip a circuit breaker?
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Because it results in a combined lowered resistance of each circuit so a greater amount of current occurs in the circuits that when overloaded is no longer safe
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What is the function of fuses or circuit breakers in a circuit?
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to prevent overloading in circuits/
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human resistance
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wet with salt water is 100 ohms, dry skin is 500,000 ohms and normal skin is 100,000 ohms
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Current and safety
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0.001 A can be felt
0.005 A painful 0.010 A involuntary muscle spasms 0.015 A loss of muscle control 0.070 A fatal if passes through heart for 1 second. |
