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2016FA PHYSICS (K. Greene) > QUIZ #2 (Ch. 8 + 17) > Flashcards

QUIZ #2 (Ch. 8 + 17) Flashcards

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1
Q

what are the two classifications of magnetic materials

A

permeability
• ease of magnetizing material

retentivity
• ability to remain magnetized

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2
Q

define: ferromagnetic
example: two materials?

A

easy to magnetize

iron, cobalt

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3
Q

define: paramagnetic
example: two materials?

A

effort to magnetize

platinum and aluminum

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4
Q

define: diamagnetic
example: one material?

A

weakly repelled by magnetic force

lead

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5
Q

three examples of nonmagnetic materials

A

wood, glass, rubber, and most materials

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6
Q

magnetic strength may be measured using all of the following except

A. Weber
B. Tesla
C. Gauss
D. Becquerel

A

D. Becquerel

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7
Q

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

A

B. poor

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8
Q

which of the following materials is most easily magnetized

A. diamagnetic
B. ferromagnetic
C. paramagnetic

A

B. ferromagnetic

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9
Q

what does Oersted’s experiment explain

A

a charge in motion will create a magnetic field

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10
Q

[*] what affects the strength of magnetism of a solenoid

A

the strength of the magnetic field is based on the number of turns/coils of wire

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11
Q

what are the three required components of electromagnetic induction

A

magnetic field

conductor

relative motion

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12
Q

methods to induce current

A

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)

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13
Q

faraday’s law

4 items

A

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

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14
Q

lenz’s law

A

induced current flow creates an opposing magnetic field

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15
Q

what are the two types of induction

A

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

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16
Q

define: mutual induction

A

two coils

varying current supplied to primary coil

induces current in secondary coil

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17
Q

define: generators

A

convert mechanical energy to electrical energy

motion and electrical field to generate power

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18
Q

what are the four components of a generator

A

armature

magnets

slip rings

brushes

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19
Q

define: motors

A

use electrical energy to convert to mechanical energy

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20
Q

what are the two types of induction motors

A

stator - electromagnets

rotor - wire windings

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21
Q

what three things control electrical current

A

transformers

autotransformers

capacitors

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22
Q

what happens between the two coils in a transformer

A

current supplied to primary coil

secondary coil in close proximity

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23
Q

step-up units what-to-what? why? current?

step down units, what-to-what? why? current?

Is _____ _____ to Ns

A

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

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24
Q

what are the three main parts of the x-ray unit

A

tube

operating console

high-voltage generator

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25
Q

[*] check blackboard for diagram - you MUST know this

A

asdasdasd

26
Q

purpose of the operating console?

what controls the quantity of the beam?

what controls the quality of the beam?

A

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

27
Q

what is line compensation?

where is the control wired into?

why is it needed?

is compensation automatic?

A

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

28
Q

what is a transformer used for?

how many coils does it use?

where is current primarily applied?

A

used to vary voltage

two coils: one primary + one secondary

AC current applied to primary coil and induces current in second coil

29
Q

what is an autotransformer?

how does it work?

when is it safer to use?

what’s its maximum voltage increase?

A

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

30
Q

what is the transformer law

A

Vs = Ns
/
Vp = Np

p = primary
s = secondary
kilovolts = 1000
volts = 1
31
Q

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

A. 500 = 220V
B. 600 = 264V
C. 300 = 132V

32
Q

what is a high voltage generator composed of

A

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)

33
Q

what is the kVp meter?

A

measures the voltage in the circuit what I would call the low voltage section (volts to kilovolts)

10V -> 10kV

34
Q

voltage increases and current _____ _____

A

voltage increases and current decreases proportionately

35
Q

quantity of radiation is primarily controlled by:

A. mA
B. keV

A

A. mA

36
Q

a transformers main function in an x-ray system is to:

A. vary DC
B. vary AC
C. increase keV
D. increase mAs

A

C. increase keV

37
Q

a step-up transformer _____

A. increases keV
B. decreases keV
C. increases mA
D. decreases mA

A

A. increases keV

also decreases amperage, option D

38
Q

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?

A

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

39
Q

how do rectifiers work

A

rectifications either turns off negative flow of electrons

if we don’t turn it off, we can redirect it

must be negative to positive

40
Q

what is a half-wave (regarding rectifiers)

A

negative portion of the wave is stopped from flowing

41
Q

what is a full-wave (regarding rectifiers)

A

negative portion is redirected into a positive direction

42
Q

what is single phase power

half-wave rectified cycles + pulses per second?

full-wave rectified cycles + pulses per second?

is single phase power efficient?

A

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

43
Q

what is three phase power

A

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

44
Q

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

A. on AC but not on DC

45
Q

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

A

D. lower than the input current

46
Q

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

A

E. Nothing

47
Q

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

A

E. Secondary side of the autotransformer

48
Q

The autotransformer has only one:

A. Coil

B. Meter

C. Rectifier

D. Switch

E. Turns ratio

A

A. Coil

49
Q

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

A

E. Is required to stabilize voltage

50
Q

The filament transformer:

A. Has four windings

B. Increases current

C. Increases voltage

D. Is an autotransformer

E. Must have precision resistors

A

B. Increases current

51
Q

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

A

D. Precision resistors

52
Q

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

A. Amplitude

53
Q

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

A

D. Increased x-ray intensity per mAs

54
Q

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

A. Electrical insulation

55
Q

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

A

C. 120 pulses per second

56
Q

[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

A

B. 100

57
Q

[RT REVIEW]

The factor that has the greatest impact on x-ray beam quality is:

A. kVp
B. mA
C. s
D. SID

A

A. kVp

58
Q

[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

A

C. 4

59
Q

[RT REVIEW]

The mAs would most likely be measured in:

A. coulombs
B. amperes
C. ohms
D. watts

A

A. coulombs

60
Q

[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

A

C. 30

61
Q

[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

A. 25

2016FA PHYSICS (K. Greene) (13 decks)

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