Flashcards in physics chapter 4 part 1 Deck (58)
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Define electrostatics
The study of stationary electric charges
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Define electrodynamics
The study of electric charges in motion aka electricity
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Know three ways an object can be electrified
◾️friction
◾️contact
◾️induction
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Define electric potential
The ability to do work because of separation of charges
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Define current
An expression of the flow of electrons in a conductor
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Define resistance
The property of an element in a circuit that resists or impedes the flow of electricity
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What is electric potential measured in?
Volts
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Define volt
The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm
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What is volt an expression of?
The difference in electric potential between two points
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What is current measured in?
Amperes
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Define ampere (& it's relationship to volt definition)
May be defined as 1 coulomb flowing by a given point in 1 second.
◾️The amount of current flowing with an electric potential of 1 volt in a circuit with a resistance of 1 ohm.
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What surrounds electrical current?
Magnetic field
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What are the 2 types of current?
◾️direct current
◾️alternating current
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What is DC?
Type of current that flows in only one direction
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How do electrons flow with DC?
Negative terminal to positive terminal
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What type of current supplies the X-ray tube?
Pulsating direct current
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What's AC?
Current that changes direction in cycles as the electric potential of the source changes
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What is resistance measured in?
Ohms
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Define ohm
The electrical difference equal to the resistance between two points along a conductor that produces a current of 1 ampere when a potential difference of 1 volts applied
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Know ohms law
Stated that the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (ampere) multiplied by the resistance
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What 4 things the amount of resistance in a conductor depends on?
◾️material
◾️length
◾️cross sectional area
◾️temperature
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What's a conductor?
Materials with an abundance of free electrons that allow a relatively free flow of electricity
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What are some examples of a conductor?
◾️copper
◾️gold
◾️water
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What's an insulator?
Has no free electrons and therefore not good conductors of electricity
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Examples of insulators
◾️rubber
◾️glass
◾️ceramic
◾️wood
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What's an electric circuit?
Closed pathway composed of wires and circuit elements through which electricity may flow
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What must happen for electricity to flow?
The pathway for electricity must be closed
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What's a closed circuit?
The pathway for electricity must be closed for electricity to flow
Switch is on
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What is an open circuit?
A circuit In which the pathway is broken, such as when a switch is turned off
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What's a battery?
A device that produces electrons through a chemical reaction, stores an electric charge for the long term and provides an electronic potential
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What's a capacitor?
It's like a battery in that it stores an electric charge but works very differently in that it can produce new electrons and stores the charge only temporarily
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What's a diode?
(Solid state rectifier) a "one way valve" device that allows electrons to flow in one direction only
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What are protective devices?
(Fuses and circuits) act as emergency device that "breaks" or open the circuit if there is a sudden surge of electricity to the circuit or device
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What's a fuse?
A section of special wire usually encased in glass that quickly melts if the current flow rises excessively thus opening the circuit
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What's a circuit breaker?
Acts like a fuse. If the flow current rises excessively the circuit breakers internal switch is tripped (opened) stopping the flow of electricity
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What's a resistor?
A device designed to inhibit the flow of electrons, thereby precisely regulating the flow of electricity through that part of the circuit where it is placed
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What's a rheostat?
An adjustable or variable form of a resistor
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What's a switch?
A device that opens a circuit (breaks the pathway)
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What's a transformer?
A device that can increase or decrease voltage by a predetermined amount
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What does ground mean?
The process of connecting the electrical device to the earth via a conductor.
Protective measure
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Where the grounding wire is connected?
Earth via a conductor
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What is magnetism?
The ability of a material to attract iron, cobalt, or nickel
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What's the three laws of magnetism?
◾️that every magnet has a north and South Pole
◾️like poles repel each other, opposite poles attract each other
◾️the force of attraction or repulsion varies directly with the strength of the poles and inversely with the square of the distance between them
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What happens to the voltage when the strength of the magnet is increased?
Increases induced voltage
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What are the 2 forms of electromagnetic induction used in xray machines?
Mutual induction and self induction
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What's mutual induction
The induction of electricity in a secondary coil by moving magnetic field
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What happens during electromagnetism when the current changes direction?
The magnetic field also changes. Previous magnetic field dies away and a new one is created that is opposite in orientation and properly oriented to the new current flow direction.
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Define Lenz's law
That an induced current flows in a direction that opposes the action that induced it.
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What is self induction?
Fluctuating magnetic field cutting back and forth through single coil, inducing a constant secondary current that opposes the original
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What are electric generators?
Devices that convert some form of mechanical energy into electrical energy
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What's an electric motor?
Device that converts electrical energy to mechanical energy through electromagnetic induction
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What are transformers?
Devices used to increase or decrease voltage (or current) through electromagnetic induction
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What's the difference between a step up and step down transformer?
◾️step down- decreases voltage, increases current
◾️step up-increases voltage, decreases current
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Know the relationship between voltage and current
Inverse
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Know what, if anything, a transformer can do with a current?
In some instances a transformer may be used to increase or decrease current
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Know what else an auto transformer can be referred to as?
kVp selector
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What's the principle an autotransformer operates under?
Self induction
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