physics chapter 4 part 1 Flashcards
Define electrodynamics
The study of electric charges in motion aka electricity
Define electrostatics
The study of stationary electric charges
Know three ways an object can be electrified
◾️friction
◾️contact
◾️induction
Define electric potential
The ability to do work because of separation of charges
Define current
An expression of the flow of electrons in a conductor
Define resistance
The property of an element in a circuit that resists or impedes the flow of electricity
What is electric potential measured in?
Volts
Define volt
The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm
What is volt an expression of?
The difference in electric potential between two points
What is current measured in?
Amperes
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.
What surrounds electrical current?
Magnetic field
What are the 2 types of current?
◾️direct current
◾️alternating current
What is DC?
Type of current that flows in only one direction
How do electrons flow with DC?
Negative terminal to positive terminal
What type of current supplies the X-ray tube?
Pulsating direct current
What’s AC?
Current that changes direction in cycles as the electric potential of the source changes
What is resistance measured in?
Ohms
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
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
What 4 things the amount of resistance in a conductor depends on?
◾️material
◾️length
◾️cross sectional area
◾️temperature
What’s a conductor?
Materials with an abundance of free electrons that allow a relatively free flow of electricity
What are some examples of a conductor?
◾️copper
◾️gold
◾️water
What’s an insulator?
Has no free electrons and therefore not good conductors of electricity
Examples of insulators
◾️rubber
◾️glass
◾️ceramic
◾️wood
What’s an electric circuit?
Closed pathway composed of wires and circuit elements through which electricity may flow
What must happen for electricity to flow?
The pathway for electricity must be closed
What’s a closed circuit?
The pathway for electricity must be closed for electricity to flow
Switch is on
What is an open circuit?
A circuit In which the pathway is broken, such as when a switch is turned off
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
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
What’s a diode?
(Solid state rectifier) a “one way valve” device that allows electrons to flow in one direction only
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
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
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
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
What’s a rheostat?
An adjustable or variable form of a resistor
What’s a switch?
A device that opens a circuit (breaks the pathway)
What’s a transformer?
A device that can increase or decrease voltage by a predetermined amount
What does ground mean?
The process of connecting the electrical device to the earth via a conductor.
Protective measure
Where the grounding wire is connected?
Earth via a conductor
What is magnetism?
The ability of a material to attract iron, cobalt, or nickel
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
What happens to the voltage when the strength of the magnet is increased?
Increases induced voltage
What are the 2 forms of electromagnetic induction used in xray machines?
Mutual induction and self induction
What’s mutual induction
The induction of electricity in a secondary coil by moving magnetic field
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.
Define Lenz’s law
That an induced current flows in a direction that opposes the action that induced it.
What is self induction?
Fluctuating magnetic field cutting back and forth through single coil, inducing a constant secondary current that opposes the original
What are electric generators?
Devices that convert some form of mechanical energy into electrical energy
What’s an electric motor?
Device that converts electrical energy to mechanical energy through electromagnetic induction
What are transformers?
Devices used to increase or decrease voltage (or current) through electromagnetic induction
What’s the difference between a step up and step down transformer?
◾️step down- decreases voltage, increases current
◾️step up-increases voltage, decreases current
Know the relationship between voltage and current
Inverse
Know what, if anything, a transformer can do with a current?
In some instances a transformer may be used to increase or decrease current
Know what else an auto transformer can be referred to as?
kVp selector
What’s the principle an autotransformer operates under?
Self induction
Describe an autotransformer (what it made of and looks like)
Only one coil of wire around a central magnetic core. Outside wires are attached at different points along the coil and induced voltage varies depending on where connections are made.
