Unit 2 (X-ray Circuit)
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the study of stationary electric charges:
the study of charges in motion:
- often considered "electricity"
a property of matter in which the smallest units are the proton (+) and the electron (-):
what is the SI unit of charge?
- (1 coulomb = 6.25x1018 electrons)
how does the conductivity of an atom increase?
with an increase in the number of free electrons within the atom
in which direction do electrons always flow?
along the path of least resistance
name some conductors we discussed (3):
name some insulators we discussed (4):
a general principle of electrostatics: like charges __________ and unlike charges ____________.
a general principle of electrostatics: the electrostatic charges between two charges is ___________ proportional to the ___________ of their quantities and __________ proportional to the __________ of the distance between them.
- directly, product
- indirectly, square
- this is Coulomb's Law
a general principle of electrostatics: electric charges reside only on the ________ surface of a __________.
a general principle of electrostatics: the concentration of charges on a ___________ surface of a __________ is greatest the __________ is __________.
- curved, conductor
- curvature, greatest
ex. curved surfaces, like the filament of the x-ray tube)
only negative charges (_________) are free to move in ________ ___________.
- solid conductors
when electrons are transferred from one object to another by rubbing the two objects together:
- ex. silk and glass rod
when electrons are transferred from a charged object to a conductor when they are touched together:
- ex. touching trampoline springs after jumping
process by which an uncharged metallic object experiences a shift of electrons when brought into electric field of a charged object:
- ex. stator and rotor of xray tube
in order for electricity to flow, a ______________________ must exist.
a distance in which electricity can transfer:
- potential difference
- ex. how your finger can be close to but not quite touching the doorknob for a static shock to occur
the ability to do work because of the separation of charges:
- electric potential
- measured in: volt (V)
the expression of the flow of electrons in a conductor:
- measured in: Ampere (I)
the property of an element in circuit that resists or impedes the flow of electricity:
- measured in: Ohm (R)
the potential difference that will maintain a current of 1ampere in a circuit with a resistance of 1 ohm:
defined as 1 coulomb flowing by a given point in 1 second:
technical factors selected when xraying:
- kVp (kilovoltage peak)
- mA (milliamperage)
a type of current that flows in both directions:
- indirect current
- (ex. generator)
a type of current that flows in only one direction:
- direct current
- (ex. battery)
what do these pictures represent?
- red is an indirect current (flowing in both directions)
- blue is a direct current (flowing in only one direction)
who discovered the inverse relationship between current and resistance?
Georg Simon Ohm
What is Ohm's Law?
- V is voltage
- I is amperage
- R is resistance
name 4 factors that affect resistance:
- cross-sectional area
how does the material affect resistance?
the fewer electrons in a material, the more resistance.
how does the length affect resistance?
longer length increases resistance
how does the cross-sectional area affect resistance?
small cross-sectional areas increase resistance
how does temperature affect resistance?
with metallic conductors, the resistance becomes greater as the temperature of the conductor rises
those materials with an abundance of free electrons that allow a relatively free flow of electricity:
conductors (loosely bound electrons)
those materials that are virtually no free electrons and are therefore very poor in the movement of electricity.
insulators (tightly bound electrons)
a closed pathway through which electricity may flow:
label the symbols:
- A. battery
- B. capacitor
- C. diode
- D. fuse
- E. switch
- F. circuit breaker
- G. resistor
- H. rheostat
- I. transformer
what is the function of a capacitor?
- it temporarily stores an electrical charge (energy)
- example: a portable x-ray unit
what is the function of a diode?
- it allows electrical flow in just one direction
- example: the x-ray tube allows flow from the anode to cathode only
what is the function of a transformer?
- it increases or decreases voltage
- example: the transformer in your home is a step-down
what is the function of a battery?
- provide electrons through a chemical reaction
- can store an electric charge long term
- provides electric potential
what is the function of a resistor?
- it inhibits the flow of electrons
- it regulates the flow of electricity in the area it is placed
what is the function of a rheostat?
- it is an adjustable of variable form of resistor, which regulates the flow of electricity/electrons
what is the function of fuses/circuit breakers?
- they break the circuit if there is a sudden surge of electricity
what is the function of a switch?
- it opens/closes a circuit
explain what "grounding" is and how it works:
- it is a process of connecting an electrical device (charged object) to earth via a conductor to neutralize it; protective
- positively charged objects take electrons from the earth until neutral, and negatively charged objects give up electrons to the earth until neutral.
magnetism is the ability of a material to attract ________, _________, and __________.
___________ are created when orbital electrons of an atom spin predominately in the same direction.
- magnetic dipoles
- negative on one side, positive on the other side
- (this magnetic force can be brought on a metal when brought in a very strong megnetic field)
magnetic fields that consist of lines of force in space:
a basic characteristics of flux: lines of flux travel from ______ to ______ inside the magnet and _______ to ________ outside the magnet.
- south pole to north pole (inside)
- north pole to south pole (outside)
a basic characteristic of flux: lines of flux in the same direction ______ each other and lines of flux in opposite directions ______ each other.
a basic characteristic of flux: magnetic fields are ________ by magnetic materials and are _________ by nonmagnetic materials.
- distorted (magnetic)
- unaffected (nonmagnetic)
list the three basic laws of magnetism:
- every magnet has a north and a south pole
- like poles repel each other and unlike poles attract each other
- the force of attraction or repulsion varies directly with the strength of the poles and inversely with the square of distance between them
what is the magnetic field measured in?
the SI unit Tesla (T)
what is the range of magnetic strengths that are used in MRI?
- from .5 to 5T (5T is currently experimental)
- the MRI turn the human body into a dipole, then sound waves are sent through to react to differing elements of the body
what is the estimated measure of the magnetic field of the Earth?
5.0x10-5 Tesla (50 micro Tesla)
list the four classifications of magnetic properties:
- nonmagnetic materials - not attracted at all by magnetic fields
- diamagnetic materials - weakly repelled by magnetic fields
- paramagnetic materials - weakly attracted to magnetic fields
- ferromagnetic materials - strongly attracted to magnetic fields
give examples of the four classifications of magnetic properties:
- nonmagnetic materials - wood, glass, plastic
- diamagnetic materials - water, mercury, gold
- paramagnetic materials - platinum, gadolinium, aluminum
- ferromagnetic materials - iron, cobalt, nickel
the most naturally diamagnetic element:
- A. paramagnetism
- B. ferromagnetism
- C. anti-ferromagnetism
- D. ferrimagnetism
___________ and ______________ are two parts of the same basic force:
Any flow of electrons is surrounded by____________.
A moving magnetic field can create _____________.
- electricity; magnetism
- a magnetic field
- an electric current
What two things were discovered by Danish physicist Hans Oersted?
- discovered a compass needle is deflected when placed near a conductor carrying an electric current
- later discovered that a solenoid (coiled wire) with an iron core can intensify
What was discovered by British scientist Michael Faraday?
discovered that a moving conductor (like a copper wire) through a magnetic field induces an electric current in that conductor (electromagnetic induction)
the phenomenon by which a current may be induced to flow in a conductor by moving that conductor through a magnetic field or by placing the conductor in a moving magnetic field:
Cutting into a magnetic field to create a current is how a ________ works.
name and define two types of electromagnetic induction used to operate x-ray equipment:
- mutual induction: the induction of electricity in a secondary coil by a moving magnetic field
- self induction: with AC, a fluctuating magnetic field, cutting back and forth through a single coil, inducing a constant secondary current that opposes the original (ex. the stator/ rotor of the x-ray tube)
converts mechanical energy to electrical energy through electromagnetic induction:
- examples: windmill turbine, dam, stream
converts electrical energy to mechanical energy through electromagnetic induction:
a device used to increase or decrease voltage (or current) through electromagnetic induction:
the change in voltage or current (amperage) through a transformer is a(n) ____________ relationship. Therefore, if voltage is increased, current _________.
name three aspects of an autotransformer:
- operates on the principle of self-induction
- has only one coil of wire around a central magnetic core which is used as both the primary and secondary coil
- outside wires tap in at various coils to provide various voltages depending on the connection made
three sections of the x-ray circuit include:
- primary circuit
- secondary circuit
- filament circuit
- A. main x-ray circuit
- B. primary circuit
- C. secondary circuit
- D. incoming power supply
- E. exposure switch
- F. autotransformer
- G. power supply to transformer
- H. step-up transformer
- I. rectifiers
- J. rheostat
- K. step-down transformer
- L. x-ray tube circuit
- M. power supply to stator
- N. filament circuit
the primary circuit consists of (5):
- main power switch (connected to incoming power)
- circuit breaker
- timer circuit
- primary side of the step-up transformer
the "on" or "off" for the unit and is connected to the main power supply to the facility
main power switch
what regulates the inconsistent supply of volts?
- the line compensator
- @220 Volts
used to protect against short circuits and electrical shock:
controlled by the radiographer through the kVp selector on the operating console, and through this, directly determines the voltage applied to the x-ray tube to produce x-rays:
what are the two types of exposure timers?
- synchronous timer
- electronic timer
Based on a synchronous motor designed to turn a shaft at 60 revolutions per second or 3600 per minute:
terminates the exposure once the capacitor recieves a programmed amount of charge:
controls the time it takes the capacitor to reach a programmed amount of charge:
- variable resistor
- (resistance decreases with shorter exposure times)
Which type of timer is the most widely used today?
electronic timer (highly sophisticated)
controls the quantity of radiation reaching the image receptor:
- AEC (Automatic Exposure Control)
- has no effect on other image characteristics like contrast
- tech must still select kVp (and mA in some cases)
Describe how the AEC works:
Consists of an ionization chamber that is placed between the patient and image receptor. As the radiation exits the patient and passes through the chamber, ionization occurs. When sufficient ionization occurs in the chamber, a signal is sent to terminator exposure. The thickness and density of the body part becomes the timer variable.
used to increase voltage from the autotransformer to kilovoltage necessary for x-ray production:
a device in the secondary circuit used to measure x-ray tube current.
converts alternating current (AC) to direct current (DC):
- stops the backward flow, so that the current flows forward only
you have to have __________ current for a transformer to work because:
- alternating (AC)
- you have to cut the flux lines
____________ flows from negative to positive.
____________ flows from positive to negative.
what is this diagram? describe what's happening in it:
- solid-state rectifier
- the "n-type" has excessive electrons, the "p-type" has holes
- the flow of electrons is always from N to P (current is opposite)
- the holes will eventually fill with negative charge, then the electrons will flow out
- it is an AC coming in through the negative side, then it changes to a DC (as holes get a negative charge, there can be no backflow)
what type of rectification will result with one diode?
what is needed to change from half-wave rectification to full wave rectification?
more diodes (at least 4)
what happens in rectification of alternating current (AC)?
the down side is eliminated.
- A. alternating current (single-phase, unrectified)
- B. atlernating current (three single-phase, unrectified)
- C. single-phase half-wave rectification (direct current)
- D. three-phase full-wave rectification (direct current)
- E. single-phase full-wave rectification (direct current)
- F. high frequency full-wave rectification (direct current)
give the percentage of ripple for the various waveforms we discussed:
- single-phase: 100%
- 3-phase 6 pulse: 13%
- 3-phase 12 pulse: 3.5%
- high frequency: less than 1%
The filament circuit begins with the ______________ which is controlled by:
- rheostat (variable resistor)
- the mA selector on the operating console
determines the number of electrons (tube current) passing through the x-ray tube during the exposure:
An increase in mA will _________ resistance.
the ___________ works with the rheostat.
- exposure timer
- (mA x sec = mAs)
The ___________________ reduces voltage but increases amperage.
Describe the effects of a high amperage. What are these effects called?
- A high amperage encourages the boiling off of electrons at the filament which increases the number of electrons sent to the anode to produce x-ray photons.
- thermionic emission
what is the final part of the filament circuit?
The smaller filament will have a ________ amount of electrons than the larger filament.
lesser (less mA)
reached when electrons on the filament offer enough potential difference to stand up and boil off the filament:
give three names of the device that allows electrons to run in only one direction:
- valve tube
- (allows from cathode to anode: negative to positive)
name the image and describe its workings:
- rectifiers: it allows electrons to run in only one direction.
- in each yellow circle (diode) is an anode side (line) and a cathode side (circle). the anode side is positive and the cathode side is negative.
- the bottom left diode has a positive charge, so it allows flow.
- the bottom right diode has a negative charge, so it doesn't allow flow.
- the top left diode has a positive charge, so it allows flow.
- the top right diode has a negative charge, so it doesn't allow flow.
- you need all four diodes for current to flow.
give the two formulas that we worked on in class, and what each part of the equation is measured in:
- V (voltage) is measured in volts:V
- I (amperage/current) is measured in amperes: amps
- R (resistance) is measured in Ohms: Ω
- P (power) is measured in wattage: watts
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