Chapter 4 Flashcards
(88 cards)
1
Q
Electrostatics
A
The study of electrostatic charges
2
Q
Electrodynamics
A
The study of electric charges in motion
3
Q
How many electrons equals 1 coulomb?
A
6.25x10^18 electrons
4
Q
What makes a good conduction? Example?
A
Movement of free electrons
Copper and gold
5
Q
What are examples of insulators?
A
Glass, plastic, wood
6
Q
Principles of Electrostatic
A
- Like charges repel, unlike charges attract
- Electric charges reside on the outside external surfaces of conductors
- Coulomb’s Low
- Concentration of charges always accumulate more on a curved surface
- Only electrons are free to move across conductors
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
8
Q
What is electric potential?
A
Ability to do do work due to a separation of charges
9
Q
What is current?
A
Flow of electrons through a conductor
10
Q
What is resistance?
A
Property that resists current or flow, makes it more difficult
11
Q
How is electric potential measured?
A
Volts
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
13
Q
Ohm’s Law
A
V = IR
14
Q
kVp determines:
A
Quality/penetration
Subject contrast
Influences contrast digitally
15
Q
What controls subject contrast in production?
A
kVp
16
Q
What controls contrast in digital imaging processing?
A
LUT
17
Q
How is current measured?
A
Amps - named after Andre Ampere
18
Q
How do electrons travel in xray tube?
A
Jump the gap between cathode to anode
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
20
Q
What is AC measurement in USA?
A
60 cycles per second/60 hz
21
Q
What is DC?
A
Current that only flows in one direction
22
Q
How is resistance measured?
A
Ohms
23
Q
How does area size affect resistance?
A
Larger area has less resistance.
24
Q
What temperatue is better for conducting of electricty?
A
Low
25
In a series circuit, what is the same across each resistor?
Current
26
In a parallel circut, what is the same across each resistor?
Voltage
27
What kind of circuit will not conduct electricity?
Open
28
What kind of circuit will conduct electricity?
Closed
29
How does a rectifier work?
Turns AC to DC
30
What are diodes?
A one way valve that help turn AC to DC in the rectifier
31
The mA selector is known as a
Rheostat
32
What is a rheostat?
A variable resistor (changes the resistance)
33
What is a transfomer?
Device that changes voltage and current
34
How does a step-up transfomer work?
Change voltage to high and current to low
35
How does a step-down transfomer work?
Changes voltage to low and current to high
36
What is electromagnetism?
Electricity and magnetism together in the same phenomenon
37
In magnets, orbital electrons predominately spin in what direction?
The same direction
38
What is flux?
Lines of force in space around a magnetic field
39
How does flux travel?
Inside - south pole to north pole
Outside - north pole to south pole
40
Lines of flux in the same direction:
repel each other
41
Lines of the flux in the opposite direction:
attract each other
42
How are magnetic fields distorted?
By other magnetic materials, but not by nonmagnetic material
43
Force of attraction or repulsion of a magnet depends on what?
Strength and distance
44
What are nonmagnetic materials and how are they attracted to magnets?
Wood, glass, plastic
Not attracted at all
45
What are diamagnetic materials and how are they attracted to magnets?
Water, gold
Slightly repelled
46
What are paramagnetic materials and how are they attracted to magnets?
Platinum, gadolinium
Slightly attracted
47
What are ferromagnetic materials and how are they attracted to magnets?
Iron, cobalt, nickel
Strongly attracted
48
What is a solenoid?
Conductor fashioned into a coil
49
What is an electromagnet?
Iron core in a solenoid
50
What 2 forms of current induction are used in x-rays?
Mutual induction and self-induction
51
What is mutual induction?
Uses 2 solenoids. The current switches direction in cycles - creating AC current
52
What is self-induction?
Only 1 solenoid. As the cycles create back and forth "cuts" across the single coil, it induses a constant secondary current (autotransfomer)
53
What do electric generators do?
Convert mechanical energy into electrical energy
54
What do electric motors do?
Covert electrical energy into mechanical energy
55
What is the most common type of transformer?
Shell core
56
3 Circuits in Xray
Primary, secondary, filament
57
What comes into the primary circuit?
220 Volts
58
What adjusts the voltage to be 220 Volts?
Line voltage compensator
59
What are the 3 types of times located in the primary circuit?
Electronic timer
mAs timer
AEC timer
60
What is included in the primary circuit?
Main power switch
Fuses
Line meter
Emergency stop
Line voltage compensator
Autotransfomer
kVp major
kVp minor
Timing switch exposure switch
kVp meter
61
What is included in the secondary circuit?
mA meter
Rectifiers
Secondary coil of step up transfomer
Tube
Ground
62
What is ripple?
Efficiency of turning AC to DC.
63
How does the secondary circuit work?
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
What are the voltage ripple precentages for single phase?
100%
65
What are the voltage ripple percentages for 3 phase?
6 pulses - 13%
12 pulses - 4%
high frequency - <1%
66
A single phase machine uses higher or lower kVp than a 3 phase?
Higher - does not expose patient to a different dose of radiation
67
What is included in the filament circuit?
mA selector/rheostat, focal spot selector, step down transfomer
68
What happens in the filament circuit?
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
What happens in the primary circuit?
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
How does mA affect resistance and the electron beam?
High mA uses large filament which creates more electrons and a larger beam.
A larger beam has less resistance (needs room to expand)
71
How many volts are in 1 kV
1000 volts = 1 kV
72
How many amps are in 1 mA
.001 amps = 1mA
73
What is a way to check your math for total ohms in parallel circuit?
Lowest ohms is always almost half of the total total resistance
74
How do you figure out total resistance in a parallel circuit?
1
___________________________
(1/R1)+(1/R2)+(1/R3)+(1/R4)
75
How do you figure out total resistance in a series circuit?
Add up ohms
R1+R2+R3+R4
76
What is the turns ratio?
Secondary turns:Primary turns
77
What is the transformer formula?
Vs = Ts = Ip
____________
Vp = Tp = Is
78
What is the magnetic domain?
Groups of similary aligned atoms formed by dipoles (atomic magnets)
79
What happens when magnetic material is placed in a magnetic field?
The domains will align with the external field. It then magnetizes the material creating a magnet
80
Shell-core has the least amount of:
Leakage flux
81
What is the efficiency rate of a shell-core transfromer?
95% efficient, 5% non efficient (leakage flux)
82
How many electrons does the small filament produce compared to large?
Small - 1x
Large - 4x
83
What does the receptor exposure control do?
Ability to change the rate of intensity
84
How many volts usually goes to the filament circuit?
8-12 volts
85
What type of generator is not used in the medical diagnostic realm?
High frequency
86
What is the highest efficiency generator we use in X-ray?
Three phase, 12 pulse
87
When using AEC, what mAs should the backup timer be set for?
150%
88
Equation for Power
P=IV or
P=I^2R
