Chapter4 Flashcards
Is the study of stationary electric charges
Electrostatic
Study of electronic charges in motion
Electrodynamics
Electrical charge is measured in
Si unit, in coulomb 6.25 x 10^18
Good conductors have
Large numbers Free electrons
Good insulators have
Few free electrons
Example of good conductors
Cooper, water, and gold
Examples of good insulators
Glass plastic ceramic and wood
Five principles electrostatic: Like charges repel and unlike charges attract
the first principle
Five principles electrostatic: Electrostatic force between two charge is directly proportional to product of their quantities and inversely proportional to the square of distance
the second principle
Five principles electrostatic: Electric charges reside only on the external surface of a conductor
the third principle
Five principles electrostatic: The concentration of charge on a curved surface of a conductor is greatest where the curvature is greatest.
the fourth principle
Only negative charges are free to move in solid conductors
Five principles electrostatic: the fifth principle
In electrostatic, electfrication of objects occur when they gain a net positive or negative charge. True of false
True
Object may be Electricfied in 3 ways 
Friction, contact, induction
True or false for electric current to an electric potential must exist
Redo this one
True
An expression of the flow of electrons in a conductor.
Current
is measured in ampere
Current
Electron potential is measured in
Volts
The property of an element in a circuit’s that resists or impedes the flow of electricity
Resistance
Resistance is measured in
Ohm
Volts is named after
Volta who invented the battery
Is the potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm
Volts
True or false volts is the expression of the difference in electric potential between two points
True
True or false Volts is also equal to the amount of work ( joules ) that can be done per unit of charge
True
Formula of volts
Volts = joules / coulombs
Is the peak kilo voltage and its selection represents the highest intensity of an X-ray photon possible for that setting
kVp
Amperes is named after
Andres Marie’s amperes, French physicist who made a significant contribution to the study of electrodynamics
Amperes is define as
1 coulomb flowing by given point in 1 second
For electric currents to flow there must be two things presents
- Potential difference between two electrodes
- Suitable medium through which it can travel
Are conductors and those resisting electric current flow are insulators
Suitable media
What two suitable medias
Vacuums and metallic conductors
Flows in one direction examples batteries
Direct current
Changes direction in cycles as the electric potential of source changes. Example electricity in homes in the u.s
Alternating current
Ohms is named after
Physicist georg Simon ohm who discovered the inverse relationship between current and resistance
➢The electrical resistance equal to the resistance between two points along a conductor that produces a current of 1 ampere when a potential difference of 1 volt is applied
Ohm
The potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) multiplied by the resistance
➢V = IR
Ohms law
V= i r
V- voltage
I - current
R- resistance
The amount of resistance in a conductor depends on four things:
Material
➢Length
➢Cross-sectional area
➢Temperature
allow free flow of current b|c they have an abundance of free electrons, when other materials have resistance b/c they do not have free electrons
Material
Resistance is directly proportional to the length of the conductor, a long conductor have more resistance than a short one
Length
Larger cross selections area Has a lower resistance than one with a small cross sectional area b/c greater external surface are which electrons can travel
Cross selections, arwa
Metallic conductors the resistance is greater as the temperature of conductors rises
Temperature
Materials with an abundance of free electrons that allow a relatively free flow of electricity
Conductors
Materials made up of atoms with tightly bound electrons that do not conduct electricity well even when attracted by a potential difference
Insulators
Materials that will conduct electricity but not as well as conductors and that will insulate but not as well as insulators
Semiconductors
is a closed pathway composed of wires and circuit elements through which electricity may flow.
Electric circuit
a closed (complete) pathway for electricity is required for electricity to flow
Close circuit
an open (broken) pathway, such as occurs when a switch is turned off
Open circuit
circuit elements are wired along a single conductor
Series circuit:
circuit elements “bridge” or branch across a conductor
Parallel circuit:
Is a complex version that has different voltage and current flowing through different sections
X-ray circuit
There are 7 electronic devices
Battery
➢Capacitor
➢Diode
➢Protective devices (fuses and circuit breakers)
➢Resistor or rheostat
➢Switch
➢Transformer
Produces electrons through a chemical reaction, stores an electric charge long term, and provides an electric potential.
Battery
Temporarily stores an electric charge and cannot produce new charges
Capacitor
A “one-way valve” device; allows electrons to flow in only one direction.
Diode
Emergency devices that break or open the circuit if there is a sudden surge of electricity to the circuit or device.
Protective devices (fuses, circuit breakers)
Is a device that Inhibits the flow of electrons, thereby precisely regulating the flow of electricity through that part of the circuit where it is placed.
Resistor
is simply an adjustable or variable form of resistor.
rheostat
A device that opens a circuit (breaks the pathway)
Switch
A device that can increase or decrease voltage by a predetermined amount.
Transformer
This is the process of connecting an electrical device to the earth via a conductor.
Grounding
Any charged object can be_________ if it is grounded.
neutralized
True or false Positively charged objects take on electrons from the earth, and negatively charged objects give up electrons to the earth until neutral.
True
True or false When activated by a “live” wire, this “short circuit” into the ground wire trips the circuit breaker, shutting off the electricity to the circuit.
True
The ability of a material to attract iron, cobalt, or nickel
Magnetism
The nature of magnetic materials is that the orbital electrons of their atoms spin in predominately_________
One direction
Atoms creat tiny magnetic called
Magnetic dipole
True or false When dipoles or “atomic magnets” form groups of similarly aligned atoms, they create magnetic domains.
True
A magnetic field consists of lines of force in space.
Flux
Flux has 3 basic characteristics
- Lines of flux travel from south pole to north pole INSIDE the magnet and from north pole to south pole OUTSIDE the magnet.
- Lines of flux in the same direction repel each other and lines of flux in the opposite direction attract each other.
- Magnetic fields are distorted by magnetic materials and are unaffected by nonmagnetic materials.
There are three laws of magnetism that may help explain electromagnetism:
- Every magnet has a north and south pole.
➢Like poles repel each other and 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.
The strength of the magnetic field is measured in the SI unit
Tesla (T).
Tesla is named after
American physicist nikola Tesla
True or false Magnetic resonance imaging (MRI) units used for medical imaging are referred to by their magnetic field strength and operate with fields from 0.5 to 5 T.
True
(e.g., glass, wood, plastic) are not attracted to magnetic fields at all
Nonmagnetic materials
(e.g., water, mercury, gold) are weakly repelled by magnetic fields.
Diamagnetic materials
(e.g., platinum, gadolinium, aluminum) are weakly attracted to magnetic fields.
Paramagnetic materials
e.g., iron, cobalt, nickel) are strongly attracted to magnetic materials.
Ferromagnetic materials
Electricity and magnetism are two parts of the same basic force.
Any flow of electrons, whether in space or in a conductor, will be surrounded by a magnetic field.
➢A moving magnetic field can create an electric current.
First identified the principle of electromagnetism
➢Later, it was discovered that the magnetic field surrounding a conductor could be intensified by fashioning it into a coil (called a solenoid)
Hans Oersted
Who Found that moving a conductor through a magnetic field induces an electric current in that conductor (called electromagnetic induction).
Michael Faraday
The induction of electricity in a secondary coil by a moving magnetic field. When a moving magnetic field is placed near a secondary coil, electricity is induced to flow in that coil
Mutual induction
Requires an understanding of Lenz’s law, which states that an induced current flows in a direction that opposes the action (the changing magnetic field) that induced it
•Self-induction
is created in a coil carrying electrical current and expands outward from the center of the coil
A magnetic field
Devices that convert some form of mechanical energy into electrical energy
Electric generators
Devices that convert electrical energy to mechanical energy through electromagnetic induction
Electric motors
Devices used to increase or decrease voltage (or current) through electromagnetic induction
Transformers
increases voltage.
A step-up transformer
decreases voltage.
step-down transformer
Transformer law for voltage:
Vs / Vp = Ns / Np (direct relationship)
Transformer law for current:
Is / Ip = Np / Ns (inverse relationship)
Relation of voltage to current in a transformer:
Is / Ip = Vp / Vs (inverse relationship)
True or false Closed-core and shell-type transformers have a ferromagnetic core to maximize efficiency.
True
Adjustable transformer controlled by Kvp selector on the operating console. Operates on the principle of self-induction and Has only one coil of wire around a central magnetic core serving as both the primary and secondary coil
Autotransformer
Consists of the main power switch, circuit breakers, the autotransformer, the timer circuit, and the primary side of the step-up transformer
Primary circuit
Consists of the secondary side of the step-up transformer, the mA meter, a rectifier bank, and the x-ray tube (except for the filaments)
Secondary circuit
Consists of a rheostat, a step-down transformer, and the filaments
Filament circuit
an on-off switch for the unit connected to the facility’s power supply
Main power switch
a device usually wired to the autotransformer that automatically adjusts the power supplied to the x-ray machine to 220 volts
Line compensator:
protect against short circuits and electric shock
Circuit breakers
used to increase the voltage from the autotransformer to the kilovoltage necessary for x-ray production
Step-up transformer:
located in this section because it is easier to control (turn on and off) a low voltage than a very high one
Timer circuit (exposure timer)
Serves the same role as timer. The patient’s body part of interest is the variable in determining when to terminate exposure
•Uses a device called an ionization chamber
Automatic exposure control (AEC) device
begins with the rest of the step-up transformer
The secondary circuit
a device placed in the secondary circuit that monitors x-ray tube current
mA meter
needed to convert AC to DC and are arranged in pairs
Rectifiers
One half of the AC cycle flows through the x-ray tube and the other half is suppressed (blocked).
Half-wave rectification
Single-phase, full-wave power
100 ripples
Three-phase, full-wave rectification
13% to 3.5% ripple
Alternating currents
Three waveforms can be phased or synchronized
High-frequency, full-wave rectification
< 1% ripple
True or false Rectifiers—the one-way valves—are necessary to route the electricity through the x-ray tube correctly
True
For a filament circuit, a variable resistor controlled by the mA selector on the operating console
Rheostat
works in concert with the rheostat; together, they determine the quantity of electrons boiled off of the filament and available for x-ray production. ( filament circuit)
Exposure timer
used in the filament circuit to increase the current by reducing the voltage that is applied to the filament
Step-down transformer
Tiny coils of wire housed in the cathode of the x-ray tube
➢Represented on the operating console by the “large focal spot” and “small focal spot”
Filament
The quantity is controlled by a_______to reflect the mA selected on the control console.
rheostat
Now we can join the two halves of the process:
We have a group, or cloud, of electrons created by the filament circuit (heating of the filament).
➢The kilovoltage applied to the x-ray tube created a large positive charge on the anode and a large negative charge on the cathode (focusing cup).
True or false The large positive charge attracts the electrons boiled off the filament, giving them tremendous kinetic energy in the process.
True
True or false The large negative charge on the cathode keeps the electrons crowded together; otherwise, they would repel each other and scatter throughout the tube.
True
True or false The electrons travel across to the anode and interact there to produce x-rays until the timer circuit terminates the process.
True
Is the property of an element in a circuit that resist or impedes the flow of electricity
Resistance
The unit of measured
A type of current that flows in only one direction.
Direct current
A battery a example of a direct current because
It has a positive and negative electrodes and when placed in an electrical circuit electrons flow from the negative terminal to the positive terminal
In the u.s the Electricity flows into homes alternates at 60 cycles per seconds. Expressed as 
Frequency of 60Hz
Examples of good semi conductors
Germanium diamond and silicon
A section of special wires usually in case in glass that quickly melts if the Current flow rises excessively thus opening the circuit
Fuse
As voltage increases the current
Decreases
X ray Circuits are divided into three circuits
Primary secondary and filaments
Milliampere parameter
Tube current
