Chapter 4 Flashcards
Electrostatics
The study of electrostatic charges
Electrodynamics
The study of electric charges in motion
How many electrons equals 1 coulomb?
6.25x10^18 electrons
What makes a good conduction? Example?
Movement of free electrons
Copper and gold
What are examples of insulators?
Glass, plastic, wood
Principles of Electrostatic
- 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
What is Coulomb’s Law?
The farther away 2 charges are, the less their force. The closer they are, the stronger their force
What is electric potential?
Ability to do do work due to a separation of charges
What is current?
Flow of electrons through a conductor
What is resistance?
Property that resists current or flow, makes it more difficult
How is electric potential measured?
Volts
What is a volt?
The potential difference that will maintain 1 current of 1 amp in a circuit with a resistance of 1 ohm
Ohm’s Law
V = IR
kVp determines:
Quality/penetration
Subject contrast
Influences contrast digitally
What controls subject contrast in production?
kVp
What controls contrast in digital imaging processing?
LUT
How is current measured?
Amps - named after Andre Ampere
How do electrons travel in xray tube?
Jump the gap between cathode to anode
What is AC?
Current of both positive and negative sine wave. Continuously chages direction in cycles.
Type of circuitry right before the tube
What is AC measurement in USA?
60 cycles per second/60 hz
What is DC?
Current that only flows in one direction
How is resistance measured?
Ohms
How does area size affect resistance?
Larger area has less resistance.
What temperatue is better for conducting of electricty?
Low
In a series circuit, what is the same across each resistor?
Current
In a parallel circut, what is the same across each resistor?
Voltage
What kind of circuit will not conduct electricity?
Open
What kind of circuit will conduct electricity?
Closed
How does a rectifier work?
Turns AC to DC
What are diodes?
A one way valve that help turn AC to DC in the rectifier
The mA selector is known as a
Rheostat
What is a rheostat?
A variable resistor (changes the resistance)
What is a transfomer?
Device that changes voltage and current
How does a step-up transfomer work?
Change voltage to high and current to low
How does a step-down transfomer work?
Changes voltage to low and current to high
What is electromagnetism?
Electricity and magnetism together in the same phenomenon
In magnets, orbital electrons predominately spin in what direction?
The same direction
What is flux?
Lines of force in space around a magnetic field
How does flux travel?
Inside - south pole to north pole
Outside - north pole to south pole
Lines of flux in the same direction:
repel each other
Lines of the flux in the opposite direction:
attract each other
How are magnetic fields distorted?
By other magnetic materials, but not by nonmagnetic material
Force of attraction or repulsion of a magnet depends on what?
Strength and distance
What are nonmagnetic materials and how are they attracted to magnets?
Wood, glass, plastic
Not attracted at all
What are diamagnetic materials and how are they attracted to magnets?
Water, gold
Slightly repelled
What are paramagnetic materials and how are they attracted to magnets?
Platinum, gadolinium
Slightly attracted
What are ferromagnetic materials and how are they attracted to magnets?
Iron, cobalt, nickel
Strongly attracted
What is a solenoid?
Conductor fashioned into a coil
What is an electromagnet?
Iron core in a solenoid
What 2 forms of current induction are used in x-rays?
Mutual induction and self-induction
What is mutual induction?
Uses 2 solenoids. The current switches direction in cycles - creating AC current
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)
What do electric generators do?
Convert mechanical energy into electrical energy
What do electric motors do?
Covert electrical energy into mechanical energy
What is the most common type of transformer?
Shell core
3 Circuits in Xray
Primary, secondary, filament
What comes into the primary circuit?
220 Volts
What adjusts the voltage to be 220 Volts?
Line voltage compensator
What are the 3 types of times located in the primary circuit?
Electronic timer
mAs timer
AEC timer
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
What is included in the secondary circuit?
mA meter
Rectifiers
Secondary coil of step up transfomer
Tube
Ground
What is ripple?
Efficiency of turning AC to DC.
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
What are the voltage ripple precentages for single phase?
100%
What are the voltage ripple percentages for 3 phase?
6 pulses - 13%
12 pulses - 4%
high frequency - <1%
A single phase machine uses higher or lower kVp than a 3 phase?
Higher - does not expose patient to a different dose of radiation
What is included in the filament circuit?
mA selector/rheostat, focal spot selector, step down transfomer
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
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
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)
How many volts are in 1 kV
1000 volts = 1 kV
How many amps are in 1 mA
.001 amps = 1mA
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
How do you figure out total resistance in a parallel circuit?
1
___________________________
(1/R1)+(1/R2)+(1/R3)+(1/R4)
How do you figure out total resistance in a series circuit?
Add up ohms
R1+R2+R3+R4
What is the turns ratio?
Secondary turns:Primary turns
What is the transformer formula?
Vs = Ts = Ip
____________
Vp = Tp = Is
What is the magnetic domain?
Groups of similary aligned atoms formed by dipoles (atomic magnets)
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
Shell-core has the least amount of:
Leakage flux
What is the efficiency rate of a shell-core transfromer?
95% efficient, 5% non efficient (leakage flux)
How many electrons does the small filament produce compared to large?
Small - 1x
Large - 4x
What does the receptor exposure control do?
Ability to change the rate of intensity
How many volts usually goes to the filament circuit?
8-12 volts
What type of generator is not used in the medical diagnostic realm?
High frequency
What is the highest efficiency generator we use in X-ray?
Three phase, 12 pulse
When using AEC, what mAs should the backup timer be set for?
150%
Equation for Power
P=IV or
P=I^2R
