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47 Cards in this Set
- Front
- Back
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Electricity
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general term for electrical phenomena, much like gravity has to do with gravitational phenomena, or sociology with social phenomena.
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Electrostatics
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The study of electric charge at rest (not in motion as in electric currents)
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Conservation of charge
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electric charge is neither created nor destroyed. The total charge before an interaction equals the total charge after.
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Coulomb's law
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The SI unit of electrical charge. One coloumb(symbol C) is equal to the total charge of 6.25 X 10^18 electrons
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Conductor
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Any material having free charged particles that easily flow through it when an electric force acts on them
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Insulator
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a material without free charged particles and through which charge does not easily flow
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Electrically polarized
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Term applied to an atom or molecule in which the charges are aligned so that one side has a slight excess of positive charge, the otehr side a slight excess of negative charge
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Electric field
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Defined as force per unit charge, it can be considered to be an aura surrounding charged objects, and is a storehouse o felectric energy. About a charged point, the field decreases with distance according to the inverse-square law, like a gravitational field. Between oppositely charged parallel plates, the electric field is uniform.
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electric potential energy
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The energy a charged object possesses by virtue of its location in an electric field
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Electric potential
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The electric potential energy per unit of charge, measured in volts, and often called voltage:
voltage = electric energy/ amount of charge |
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Volt
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The unit of electric potential; 1 volt = 1 joule per coulomb
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capacitor
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an electrical device, in its simplest form a pair of parallel conducting plates separated by a small distance, that stores electric charge and energy
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What part of an atom is positively charged and what part is negatively charged?
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The nucleus is positively charged while the surrounding electrons are negatively charged
protons are positively charged while electrons are negatively charged |
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How does the charge of one electron compare to that of another electron?
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All electrons are identical , they have the same mass and same quantity of negative charge.
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How do the masses of electrons compare to the masses of protons? Neutrons?
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A proton has 2000 times the mass of an electron but its positive charge is equal in magnitude to the negative charge of the electron. A neutron has slightly greater mass than a proton and has no charge.
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How do the numbers of protons in the atomic nucleus normally compare to the number of electrons that orbit the nucleus
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atoms usually have as many electrons as protons, so the atom has zero net charge.
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What kind of charge does an object acquire when electrons are stripped from it?
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A positive charge
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What is a positive ion? A negative ion?
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A charged atom is an ion,
A positive ion has a net positive charge and a negative ion has a net negative charge. |
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What is meant by saying charge is conserved?
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When electrons are simply transferred from one material to another, not created or destroyed.
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What is meant by saing charge is quantized?
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The elementary unit of charge is called quanta, there is a whole number multiple of the charge of an electron, so we say that charge is quantized, with the smallest quantum of charge being that of the electron or proton. No smaller units of charge have been found.
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What particle has exactly one quantum unit of charge?
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electrons
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How does a coulomb of charge compare to the charge of a single electron?
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1 coulomb is associated with 6.25 billion billion electrons
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How is Coulomb's law similar to Newton's law of gravitation? How is it different?
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The proportionality constant k in coulomb's law is similar to G in Newton's law of gravitation. However, instead of being very small number like G (6.67 X 10^-11), the electrical proportionality constant K is a very large number, k= 9,000,000,000 NXm^2/C^2
Newton's law of gravitation for massive bodies is similar to Coulomb's law for electrically charged bodies. Whereas the the gravitational force of attraction between particles such as an electron and a proton is extremely small , the electrical force between these particles is relatively enromous. Another important difference: in electrical foces there is either an attractive or repulsive, whie in gravitational forces there are only attractive. |
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The proportionality constant k in Coulomb's law is huge in ordinary units, whereas the proportionality constant G in Newton's law of gravitation is tiny. What does this mean for the relative strengths of these two forces?
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The electrical chaged bodies of coulomb's law is much stronger.
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How does the magnitude of electrical force between a pair of charged objects change when the objects are moved twice as far apart? Three times as far apart?
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Coulombs law states that for two charged objects that are much smaller than the distance between them, the force between the two objects varies directly as the product of their chrages and inversely as the square of the separation distance
so the law is F = k (q1q2)/d^2 the electrical force decreases inversely as the square of the distance between charged bodies |
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The inverse-square law pg. 147
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The dilution of the force of gravity or electrical forces by distance, ie throughing paint from a can will spread out more and more the greater the distance in square units,
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Why are metals good conductors of both heat and electricity?
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Because electrons in their outer atomic shell are "loose", or not anchored to the nuclei of atoms and wander in the material so they can conduct heat and electric currents
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Why are materials such as glass and rubber good insulators?
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Because they are poor conductors of electricity and heat due to their tightly bound electrons to atoms.
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How does a semiconductor differ from a conductor or an insulator?
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Semiconductors are neither good insulators nor good conductors. and fall in the middle of the electrical resistivity.
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What is a transistor, and what are some of its functions?
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They are thin layers of semiconducting materials sandwiched together, they are used to control the flow of currents in circuits, to detect and amplify radio signals, and to produce oscillations in transmitters; they also act as digital switches
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How much electrical resistance does a superconductor have to a flow of electric charge?
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They have zero resistance to the flow of charge as tehy have acquired infinite conductivity
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What happens to electrons in any charging process?
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They are transferred from one place to another, simply by touching
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Give an example of something charged by friction
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scuffing our shoes across a room and getting a shock when you touch the doornob
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Give two examples of common force fields.
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gravitational field, and electric field
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how is the direction of an electric field defined?
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shown by vectors and is defined to be the direction in which a small positive test charge at rest would be moved.
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How is the magnitude of an electric field defined?
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The magnitued is the force per unit of charge.
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Why is there no electric field in the middle of a charged spherical conductor?
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because the net force on teh test charge inside the conductor is zero the electric field is therefore zero.
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Does an electric field exist within a charged spherical conductor at points other than its center?
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no it doesn't, this is understood through geometry and the invese square law
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When charges mutually repel and distribute themselves on the surface of conductors, what is the effect inside the conductor?
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basically the electrons produce a zero field inside the conductor because it must reach equilibrium
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What is the electric field inside a car struck by lightning?
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the net electric field inside the car is practically zero.
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Distinguish between electric potential energy and electric potential
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The energy the particle possesses by virtue of its location is electric potential energy while electric potential = electric potential energy/ charge
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A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy? Explain.
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No, even though the voltae is high the electric potential energy is low because of the small amount of charge.
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Why does a charged capacitor have a net charge of zero?
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Because the capacitor consists of two closely spaced metal parallel plates. When connected to a battery, the plates acquire equal and opposite charges. The voltage between the plates then matches the electric potential difference between the battery terminals.
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Where is the stored energy in a capacitor?
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in the electric field between its plates
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In order to store more energy in a capacitor, how might you change the capacitor?
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perhaps make the space between plates bigger
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What is the magnitude of the electric field inside the dome of a charged Van De Graaf generator?
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Zero
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Why does Meidor's hair stand out in fig 21.31?
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she is touching the high volatage on the sphere because the voltages accelerate charge particles that can be used as projectiles for penetrate the nuclei of atoms.
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