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Radiologic Physics > Chapter 4 > Flashcards

Chapter 4 Flashcards

1
Q

Electrostatics

A

The study of electrostatic charges

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2
Q

Electrodynamics

A

The study of electric charges in motion

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3
Q

How many electrons equals 1 coulomb?

A

6.25x10^18 electrons

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4
Q

What makes a good conduction? Example?

A

Movement of free electrons

Copper and gold

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5
Q

What are examples of insulators?

A

Glass, plastic, wood

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6
Q

Principles of Electrostatic

A
  1. Like charges repel, unlike charges attract
  2. Electric charges reside on the outside external surfaces of conductors
  3. Coulomb’s Low
  4. Concentration of charges always accumulate more on a curved surface
  5. Only electrons are free to move across conductors
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7
Q

What is Coulomb’s Law?

A

The farther away 2 charges are, the less their force. The closer they are, the stronger their force

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8
Q

What is electric potential?

A

Ability to do do work due to a separation of charges

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9
Q

What is current?

A

Flow of electrons through a conductor

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10
Q

What is resistance?

A

Property that resists current or flow, makes it more difficult

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11
Q

How is electric potential measured?

A

Volts

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12
Q

What is a volt?

A

The potential difference that will maintain 1 current of 1 amp in a circuit with a resistance of 1 ohm

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13
Q

Ohm’s Law

A

V = IR

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14
Q

kVp determines:

A

Quality/penetration
Subject contrast
Influences contrast digitally

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15
Q

What controls subject contrast in production?

A

kVp

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16
Q

What controls contrast in digital imaging processing?

A

LUT

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17
Q

How is current measured?

A

Amps - named after Andre Ampere

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18
Q

How do electrons travel in xray tube?

A

Jump the gap between cathode to anode

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19
Q

What is AC?

A

Current of both positive and negative sine wave. Continuously chages direction in cycles.

Type of circuitry right before the tube

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20
Q

What is AC measurement in USA?

A

60 cycles per second/60 hz

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21
Q

What is DC?

A

Current that only flows in one direction

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22
Q

How is resistance measured?

A

Ohms

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23
Q

How does area size affect resistance?

A

Larger area has less resistance.

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24
Q

What temperatue is better for conducting of electricty?

A

Low

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25
Q

In a series circuit, what is the same across each resistor?

A

Current

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26
Q

In a parallel circut, what is the same across each resistor?

A

Voltage

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27
Q

What kind of circuit will not conduct electricity?

A

Open

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28
Q

What kind of circuit will conduct electricity?

A

Closed

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29
Q

How does a rectifier work?

A

Turns AC to DC

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30
Q

What are diodes?

A

A one way valve that help turn AC to DC in the rectifier

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31
Q

The mA selector is known as a

A

Rheostat

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32
Q

What is a rheostat?

A

A variable resistor (changes the resistance)

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33
Q

What is a transfomer?

A

Device that changes voltage and current

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34
Q

How does a step-up transfomer work?

A

Change voltage to high and current to low

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35
Q

How does a step-down transfomer work?

A

Changes voltage to low and current to high

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36
Q

What is electromagnetism?

A

Electricity and magnetism together in the same phenomenon

37
Q

In magnets, orbital electrons predominately spin in what direction?

A

The same direction

38
Q

What is flux?

A

Lines of force in space around a magnetic field

39
Q

How does flux travel?

A

Inside - south pole to north pole

Outside - north pole to south pole

40
Q

Lines of flux in the same direction:

A

repel each other

41
Q

Lines of the flux in the opposite direction:

A

attract each other

42
Q

How are magnetic fields distorted?

A

By other magnetic materials, but not by nonmagnetic material

43
Q

Force of attraction or repulsion of a magnet depends on what?

A

Strength and distance

44
Q

What are nonmagnetic materials and how are they attracted to magnets?

A

Wood, glass, plastic

Not attracted at all

45
Q

What are diamagnetic materials and how are they attracted to magnets?

A

Water, gold

Slightly repelled

46
Q

What are paramagnetic materials and how are they attracted to magnets?

A

Platinum, gadolinium

Slightly attracted

47
Q

What are ferromagnetic materials and how are they attracted to magnets?

A

Iron, cobalt, nickel

Strongly attracted

48
Q

What is a solenoid?

A

Conductor fashioned into a coil

49
Q

What is an electromagnet?

A

Iron core in a solenoid

50
Q

What 2 forms of current induction are used in x-rays?

A

Mutual induction and self-induction

51
Q

What is mutual induction?

A

Uses 2 solenoids. The current switches direction in cycles - creating AC current

52
Q

What is self-induction?

A

Only 1 solenoid. As the cycles create back and forth “cuts” across the single coil, it induses a constant secondary current (autotransfomer)

53
Q

What do electric generators do?

A

Convert mechanical energy into electrical energy

54
Q

What do electric motors do?

A

Covert electrical energy into mechanical energy

55
Q

What is the most common type of transformer?

A

Shell core

56
Q

3 Circuits in Xray

A

Primary, secondary, filament

57
Q

What comes into the primary circuit?

A

220 Volts

58
Q

What adjusts the voltage to be 220 Volts?

A

Line voltage compensator

59
Q

What are the 3 types of times located in the primary circuit?

A

Electronic timer
mAs timer
AEC timer

60
Q

What is included in the primary circuit?

A

Main power switch
Fuses
Line meter
Emergency stop
Line voltage compensator
Autotransfomer
kVp major
kVp minor
Timing switch exposure switch
kVp meter

61
Q

What is included in the secondary circuit?

A

mA meter
Rectifiers
Secondary coil of step up transfomer
Tube
Ground

62
Q

What is ripple?

A

Efficiency of turning AC to DC.

63
Q

How does the secondary circuit work?

A

Primary coil of the step up transfomer gets exactly 220V, it then steps it up to the secondary coil.

It creates the kVp you choose

kVp goes through a rectifier. Turns AC to DC. Zaps electrons from cathode side to anode

64
Q

What are the voltage ripple precentages for single phase?

A

100%

65
Q

What are the voltage ripple percentages for 3 phase?

A

6 pulses - 13%
12 pulses - 4%
high frequency - <1%

66
Q

A single phase machine uses higher or lower kVp than a 3 phase?

A

Higher - does not expose patient to a different dose of radiation

67
Q

What is included in the filament circuit?

A

mA selector/rheostat, focal spot selector, step down transfomer

68
Q

What happens in the filament circuit?

A

Rheostat is controlled by mA selector on console

This controls the current that is applied to the filament and directly related to the number of electrons boiled off

The step down transfomer decreases voltage and increases current. Turns amperage to mA

mA goes to the mA meter and the filament circuitry in the cathode

69
Q

What happens in the primary circuit?

A

Voltage comes in and gets measured by the line meter. Compensator adjusts voltage to be exaclty 220V

Autotransfromer adjusts its coils up and down to deliver voltage to both step up and step down

70
Q

How does mA affect resistance and the electron beam?

A

High mA uses large filament which creates more electrons and a larger beam.

A larger beam has less resistance (needs room to expand)

71
Q

How many volts are in 1 kV

A

1000 volts = 1 kV

72
Q

How many amps are in 1 mA

A

.001 amps = 1mA

73
Q

What is a way to check your math for total ohms in parallel circuit?

A

Lowest ohms is always almost half of the total total resistance

74
Q

How do you figure out total resistance in a parallel circuit?

A

1
___________________________
(1/R1)+(1/R2)+(1/R3)+(1/R4)

75
Q

How do you figure out total resistance in a series circuit?

A

Add up ohms
R1+R2+R3+R4

76
Q

What is the turns ratio?

A

Secondary turns:Primary turns

77
Q

What is the transformer formula?

A

Vs = Ts = Ip
____________
Vp = Tp = Is

78
Q

What is the magnetic domain?

A

Groups of similary aligned atoms formed by dipoles (atomic magnets)

79
Q

What happens when magnetic material is placed in a magnetic field?

A

The domains will align with the external field. It then magnetizes the material creating a magnet

80
Q

Shell-core has the least amount of:

A

Leakage flux

81
Q

What is the efficiency rate of a shell-core transfromer?

A

95% efficient, 5% non efficient (leakage flux)

82
Q

How many electrons does the small filament produce compared to large?

A

Small - 1x
Large - 4x

83
Q

What does the receptor exposure control do?

A

Ability to change the rate of intensity

84
Q

How many volts usually goes to the filament circuit?

A

8-12 volts

85
Q

What type of generator is not used in the medical diagnostic realm?

A

High frequency

86
Q

What is the highest efficiency generator we use in X-ray?

A

Three phase, 12 pulse

87
Q

When using AEC, what mAs should the backup timer be set for?

A

150%

88
Q

Equation for Power

A

P=IV or
P=I^2R

Radiologic Physics (9 decks)

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