Chapter 4 Exam Flashcards
difference in electric potential, energy in a circuit
volt
electrons flow in only one direction
ex: batteries
direct current (DC)
electrons flow in one direction for the first half of the cycle and then in the other for the second half of the cycle
ex: U.S. current (60 Hz)
positive cycle: 1/120 second
alternating current (AC)
closed pathway composed of wires and circuit elements through which electricity may flow
electric circuit
which circuit do we use in x-ray?
series circuit
device that opens a circuit (breaks the pathway)
switch
device that can increase or decrease voltage by a predetermined amount
transformer
Voltage goes back and forth
Operates on the principle of self-induction
Has only one coil of wire around a central magnetic core serving as both the primary and secondary coil
auto transformer
part of the transformer that increases voltage
step-up
part of transformer that decreases voltage, turns it into milliamperage (mA), increases heat
step-down
devices that convert electrical energy to mechanical energy through electromagnetic energy
electric motors
what are the 3 parts of the x-ray circuit?
primary, secondary, filament
anode side, 220 volts come in and hit the switch which changes the volts to the same number as the set kVp (ex: 70 kVp = 70 volts), timer circuit, primary side of step-up transformer
primary circuit
anode side, changes the number of volts to kilovolts (ex: 70 volts = 70 kilovolts), secondary side of step-up transformer, entire x-ray tube except for filament
secondary circuit
cathode side, the mA meter, consists of rheostat, a step-down transformer and filaments, tiny coils of wire housed in the cathode of the x-ray tube
represented by the large and small focal spot
filament circuit
electrons boiling off filament is called
thermionic emission
more x-rays being created on the cathode side
anode heel effect
if you increase kVp by ___ it is the same as doubling your mass
15% (rule)
true or false? photons and x-rays are the same thing
true
raising kVp creates higher quality x-ray photons which allows them to:
get through the 2.5mm aluminum equivalent filter where x-rays come out, instead of being trapped
the study of electric charges
electrostatics
what are electrical charges measured in?
coulombs
1 coulomb is equal to the electrical charge of _________ electrons
6.25 x 10^18
good conductors have a _____ number of free electrons and good insulators have ____ free electrons
large, few
The electrostatic force
between two charges is
directly proportional to the
product of their quantities and inversely proportional to the square of the distance between them
coulomb’s law
law of electrostatics
like charges repel and unlike charges attract
only negative charges are free to move in solid containers
electrical charges reside externally
the study of electric charges in motion; what we think of as “electricity”
electrodynamics
the ability to do work because of a separation of charges; electrons will flow from abundance to deficiency
electric potential
Electrons bunched up on one end of a conductor creates an ______ ______ because the repulsive force causes some electrons to move so that work can be done
electric potential
The ability to do work due to a separation of charges
electric potential (volt)
An expression of the flow of electrons in a conductor
current (ampere)
The property of an element in a circuit that resists or impedes the flow of electricity
resistance (ohm)
a volt is the ratio of _____ to _______
joules to coulombs
volt = joules/coulombs
For electric current to flow, the following must be
present:
A potential difference between two electrodes
A suitable medium through which it can travel
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
resistance (ohm Ω)
the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) multiplied by the resistance
ohms law
voltage = I (current) x R (resistance)
what are the 4 factors of resistance?
- the material
- length (increase length = increase resistance)
- cross-sectional diameter
- 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
a _____ (complete) pathway for electricity is required for electricity to flow
closed circuit
an ____ (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
Total voltage is equal to
total current x total resistance:
V(T) =I(T) x R(T)
Resistance is equal to
the sum of the individual resistances:
R(T) = R(1) + R(2) + R(3)
Current is equal throughout
throughout the circuit:
I(T) = I(1) = I(2) = I(3)
Voltage is equal to
the sum of the individual voltages:
V(T) = V(1) + V(2) + V(3)
Total resistance is inversely
proportional to
the sum of the reciprocals of each individual resistance: 1/R(T) = 1/R(1) + 1/R(2) + 1/R(3)
Produces electrons through a chemical reaction, stores an electric charge long term, and provides an electric potential
battery
temporarily stores an electric charge
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)
Inhibits the flow of electrons, thereby precisely regulating the flow of electricity through that part of the circuit where it is placed.
Resistor (and rheostat)
A device that opens a circuit
(breaks the pathway)
switch
A device that can increase or
decrease voltage by a
predetermined amount
Transformer
An object may be electrified in 3 ways:
friction, contact, induction
a process of connecting the electrical device to the earth via a conductor, is a protective measure
grounding
Any charged particle in
motion creates a _______ _____
magnetic field
The magnetic field of a
charged particle in
motion is _________ to the motion of that particle
perpendicular
A magnetic field consists of lines of
force in space.
Lines of this travel from south pole to north pole inside the magnet and from north pole to south pole outside the magnet.
flux
The strength of the
magnetic field is measured in the
SI unit Tesla (T)
who first identified the
principle of electromagnetism?
Hans Oersted
who found that moving a conductor through a magnetic field induces an electric current in that conductor (called electromagnetic induction)?
Michael Faraday
Wire wrapped around iron
core
Electric current creates
magnetic field
Intensity of the field is
proportional to the electric
current
Iron core increases intensity
of the magnetic field lines
properties of electromagnets
What is it called when a moving
magnetic field (created by AC) is placed near a secondary coil, and
electricity is induced to flow in the secondary coil
mutual induction
an induced current flows in a direction that opposes the action (the changing magnetic field) that induced it
Lenz’s law
Magnitude of induced electromagnetic force (emf) depends on 4 factors
Faraday’s law of electromagnetic induction
what are the 4 factors of Faraday’s law of electromagnetic induction
- strength
- velocity
- angle
- # of turns
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
transformer law for voltage:
V(s) / V(p) = N(s) / N(p)
(direct relationship)
transformer law for current:
(inverse relationship)
I(s) / I(p) = N(p) / N(s)
relation of voltage to current in a transformer:
(inverse relatioinship)
I(s) / I(p) = V(p)/ V(s)
_______ and _______ transformers have a
ferromagnetic core to maximize efficiency
Closed-core, shell-type
an on-off switch for the unit
connected to the facility’s power supply
(in primary circuit)
main power switch
a device usually wired to the
autotransformer that automatically adjusts the power supplied to the x-ray machine to 220 volts
(in primary circuit)
line compensator
protect against short circuits and electric shock
(in primary circuit)
circuit breakers
an adjustable transformer
controlled by the kilovolt peak (kVp) selector on the
operating console
(in primary circuit)
autotransformer
____ ______ _______ ensures consistent voltage to the x-ray tube and circuit (220 V AC)
line voltage compensator
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
Provide correct exposure regardless of patient size & reduce repeats
The patient’s body part of interest is the variable in determining when to terminate exposure
Uses a device called an ionization chamber
Three ion chambers placed between the patient and the image receptor
Automatic exposure control (AEC) device
It can “make” or
“break” the high
voltage across the
x-ray tube.
Most monitor mAS
for termination
guard timer (6s)
a device placed in the secondary circuit that monitors x-ray tube current
mA meter
what are the parts of the secondary circuit?
step-up transformer
rectification circuit
mA meter
x-ray tube
Solid state devices that allow
current to flow in only one
direction
converts AC to DC
occurs after the
step-up transformer and
before the x-ray tube
rectifiers
X-ray tubes must operate with _______ which will only allow e- flow from cathode (+) to anode (-). Otherwise, filament would be destroyed
direct current (DC)
Requires at least 4 diodes
Negative ½
reversed – anode always positive
2 diodes conduct during positive ½
2 diodes conduct during negative ½
Exposure time ½
full wave rectification
Rectifiers are arranged in pairs (0, 1, or 2 diodes)
One half of the AC cycle flows through the x-ray tube and the other half is suppressed (blocked)
Wastes ½ power & requires 2 x exposure
half-wave rectification
Three waveforms can be phased or synchronized
alternating currents
Three-phase, full-wave rectification
what % ripple?
13% to 3.5% ripple
High-frequency, full-wave rectification
what % ripple?
< 1% ripple
what are the parts of the filament circuit?
rheostat, exposure timer, step-down transformer
fixed precision resistors that
reduce voltage to a value that = selected m
rheostats
what are the parts/properties of the filament?
coil of tungsten wire
thermionic emission
space charge effect
An x-ray tube is an example of current flow in a/an:
vaccum
Which of the following increases or decreases voltage by a fixed amount?
transformer
Which of the following is Coulomb’s law?
Electrostatic force between charges is directly proportional to product of quantities and inversely proportional to square of distance between them
A rheostat will:
vary resistance
In a metallic conductor:
Electrons move on external surface
Nearly al discussion of electricity deals with the movement of:
Negative charges
Which of the following conditions or environments will provide the least resistance?
Large cross-sectional area
The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm is the definition of:
Volt
The removal of electrons from an object by rubbing it with another is electrification by:
Friction
Which of the following allows electrons to flow in only one direction?
Diode
Which of the following is a unit of measure of current?
Ampere
Magnetic flux is:
Curved lines of force in space
What is the magnetic classification of materials weakly attracted to magnets?
Paramagnetic
The unit of measure for electric potential is:
V
An ______ is an adjustable or variable form of resistor.
rheostat
