QUIZ #2 (Ch. 8 + 17) Flashcards
what are the two classifications of magnetic materials
permeability
• ease of magnetizing material
retentivity
• ability to remain magnetized
define: ferromagnetic
example: two materials?
easy to magnetize
iron, cobalt
define: paramagnetic
example: two materials?
effort to magnetize
platinum and aluminum
define: diamagnetic
example: one material?
weakly repelled by magnetic force
lead
three examples of nonmagnetic materials
wood, glass, rubber, and most materials
magnetic strength may be measured using all of the following except
A. Weber
B. Tesla
C. Gauss
D. Becquerel
D. Becquerel
if a metal bar is easily magnetized, it is said to have excellent permeability, it would also have ___ retentivity
A. excellent
B. poor
C. no correlation
B. poor
which of the following materials is most easily magnetized
A. diamagnetic
B. ferromagnetic
C. paramagnetic
B. ferromagnetic
what does Oersted’s experiment explain
a charge in motion will create a magnetic field
[*] what affects the strength of magnetism of a solenoid
the strength of the magnetic field is based on the number of turns/coils of wire
what are the three required components of electromagnetic induction
magnetic field
conductor
relative motion
methods to induce current
move a conductor through a stationary magnetic field
move magnetic lines of force across conductor
vary the strength of a stationary magnetic field through a conductor
(you have to move either the field or conductor to induce current)
faraday’s law
4 items
1) Strength of magnetic field
2) Speed of motion between lines of force and conductor
3) Angle between lines of flux and conductor (90° is optimal)
4) Number of turns in conductor
lenz’s law
induced current flow creates an opposing magnetic field
what are the two types of induction
mutual induction
self-induction (useless info): in a coil of wire, the electrons in one coil can affect the coil of wire next to it
define: mutual induction
two coils
varying current supplied to primary coil
induces current in secondary coil
define: generators
convert mechanical energy to electrical energy
motion and electrical field to generate power
what are the four components of a generator
armature
magnets
slip rings
brushes
define: motors
use electrical energy to convert to mechanical energy
what are the two types of induction motors
stator - electromagnets
rotor - wire windings
what three things control electrical current
transformers
autotransformers
capacitors
what happens between the two coils in a transformer
current supplied to primary coil
secondary coil in close proximity
step-up units what-to-what? why? current?
step down units, what-to-what? why? current?
Is _____ _____ to Ns
step-up: volts to kilovolts (more)
• the number of turns—when greater on secondary coil— this is step-up
– current goes down (amperes)
step-down: kilovolts to volts (less)
• the number of turns—when greater on primary coil—this is step-down
– current goes up (amperes)
Is inversely proportional to Ns
I = current
what are the three main parts of the x-ray unit
tube
operating console
high-voltage generator
[*] check blackboard for diagram - you MUST know this
asdasdasd
purpose of the operating console?
what controls the quantity of the beam?
what controls the quality of the beam?
allows tech to control x-ray tube current and voltage
QUANTITY of the beam is controlled by mAs–refers to number of x-rays (high/low mAs)
• if you double the mAs, twice as many x-rays go through patient
QUALITY of the beam is controlled by kVp—refers to penetrability of the beam (high/low kVp)
• there’s a range of energy: p = peak/potential of power
what is line compensation?
where is the control wired into?
why is it needed?
is compensation automatic?
measures voltage at the tube and uses a control to adjust that voltage to 220v if 220v is needed for exposure
the control is wired into the autotransformer
needed due to power companies inability to sustain 220v at all times, any fluctuation in voltage will adversely affect tube function
compensation is automatically performed on newer units
what is a transformer used for?
how many coils does it use?
where is current primarily applied?
used to vary voltage
two coils: one primary + one secondary
AC current applied to primary coil and induces current in second coil
what is an autotransformer?
how does it work?
when is it safer to use?
what’s its maximum voltage increase?
provides x-ray machines with high-voltage circuit with a precise/constant voltage
gives the option to include more/less coils for step-up and step-down
(safer to do fine-tuning in the autotransformer)
maximum of 2x voltage
what is the transformer law
Vs = Ns
/
Vp = Np
p = primary s = secondary
kilovolts = 1000 volts = 1
autotransformer is supplied with the 220V to the primary connection, which encloses 500 windings, what will be the secondary voltage across the following secondary connections
A. 500
B. 600
C. 300
A. 500 = 220V
B. 600 = 264V
C. 300 = 132V
what is a high voltage generator composed of
high-voltage transformer
filament transformer
rectifiers - we need AC at first and then turn it into DC (keeps one end always negative and one end always positive to keep flow of electrons going)
what is the kVp meter?
measures the voltage in the circuit what I would call the low voltage section (volts to kilovolts)
10V -> 10kV
voltage increases and current _____ _____
voltage increases and current decreases proportionately
quantity of radiation is primarily controlled by:
A. mA
B. keV
A. mA
a transformers main function in an x-ray system is to:
A. vary DC
B. vary AC
C. increase keV
D. increase mAs
C. increase keV
a step-up transformer _____
A. increases keV
B. decreases keV
C. increases mA
D. decreases mA
A. increases keV
also decreases amperage, option D
what physical part of the x-ray machine controls mA
increase in temp = _____ in electron emission
[*] how many total amps are usually sent to it?
filament temperature controls the number of electrons emitted (that is controlled by the current supplied to the tube)
increase in temp = increase in electron emission
[*] we usually send about 3-6 total amps into the filament of wire
how do rectifiers work
rectifications either turns off negative flow of electrons
if we don’t turn it off, we can redirect it
must be negative to positive
what is a half-wave (regarding rectifiers)
negative portion of the wave is stopped from flowing
what is a full-wave (regarding rectifiers)
negative portion is redirected into a positive direction
what is single phase power
half-wave rectified cycles + pulses per second?
full-wave rectified cycles + pulses per second?
is single phase power efficient?
pulsing x-ray beam due to alternating current from zero to peak
half-way rectified = one pulse per cycle
60 cycles in a second = 60 pulses a second
full-wave rectified = two pulses per cycle
60 cycles in a second = 120 pulses a second
it is NOT effeicient
what is three phase power
three individual waves being sent out that are slightly out of sync with each other such that current never has to reach zero
3 phase, 6 pulse = full-wave rectified, we know it’s 6 pulses per cycle and 360 pulses per second
3 phase, 12 pulses = full-wave rectified, we know it’s 12 pulses in a cycle times 60 cycles a second gets us to 720 pulses per second
The transformer changes:
A. on AC but not on DC
B. on both DC and AC
C. on DC but not on AC
D. only above its critical current
E. only on a constant voltage
A. on AC but not on DC
The output current in a step-up transformer is:
A. higher than the input current
B. independent of the input current
C. independent of the turns ratio
D. lower than the input current
E. the same as the input current
D. lower than the input current
If DC is applied to the primary coil of a step-up transformer, what is the result in the secondary coil?
A. AC
B. Increased current
C. Increased magnetic field
D. Increased voltage
E. Nothing
E. Nothing
Power to the primary side of the high-voltage transformer comes from the:
A. Filament transformer
B. Line-voltage compensator
C. Primary side of the autotransformer
D. Rectifier
E. Secondary side of the autotransformer
E. Secondary side of the autotransformer
The autotransformer has only one:
A. Coil
B. Meter
C. Rectifier
D. Switch
E. Turns ratio
A. Coil
Line compensation:
A. Adjusts the line frequency to 60 Hz
B. Compensates for rectification
C. Is necessary for proper exposure timing
D. Is necessary to convert AC to DC
E. Is required to stabilize voltage
E. Is required to stabilize voltage
The filament transformer:
A. Has four windings
B. Increases current
C. Increases voltage
D. Is an autotransformer
E. Must have precision resistors
B. Increases current
The design of fixed mA stations requires the use of which of the following?
A. A center-tapped meter
B. DC power
C. Major and minor taps
D. Precision resistors
E. Primary and secondary windings
D. Precision resistors
A change in the voltage waveform from the primary side to the secondary side of the high-voltage transformer produces a change in:
A. Amplitude
B. Frequency
C. Phase
D. Velocity
E. Wavelength
A. Amplitude
Which of the following is an advantage of three-phase power over single-phase power?
A. Improved spatial resolution
B. Increased kVp
C. Increased mAs
D. Increased x-ray intensity per mAs
E. Lower capital cost
D. Increased x-ray intensity per mAs
Oil is used in the high-voltage section of an x-ray imaging system for which of the following functions?
A. Electrical insulation
B. Reduction of rotor friction
C. Reduction of voltage ripple
D. Thermal conduction
E. Voltage rectification
A. Electrical insulation
If 60 Hz AC power is full-wave rectified, output voltage consists of:
A. 60 pulses per second
B. 90 pulses per second
C. 120 pulses per second
D. 70% ripple
E. Zero ripple
C. 120 pulses per second
[RT REVIEW]
Doubling the x-ray tube current most likely increases the number of x-ray photons by __ %.
A. 50
B. 100
C. 150
D. 200
B. 100
[RT REVIEW]
The factor that has the greatest impact on x-ray beam quality is:
A. kVp
B. mA
C. s
D. SID
A. kVp
[RT REVIEW]
The minimal percentage change in kVp that would result in a clearly visible change in film density is most likely __ %.
A. 1
B. 2
C. 4
D. 8
C. 4
[RT REVIEW]
The mAs would most likely be measured in:
A. coulombs
B. amperes
C. ohms
D. watts
A. coulombs
[RT REVIEW]
The percentage change in mAs that would result in a clearly visible change in film density is most likely __ %.
A. 3
B. 10
C. 30
D. 100
C. 30
[RT REVIEW]
If the distance from an x-ray tube doubles, the relative x-ray intensity is __ %.
A. 25
B. 50
C. 200
D. 400
A. 25
