a coil of wire that carries current & has a core of iron inserted in its center to increase magnetic strength
What is true about the interactions between the lines of force & a single loop conductor?
1. the stronger the magnetic field, the higher the induced voltage
2.if the number of turns in the conductor is increased, the induced voltage increases
The physical contact of two or more non-insulated wires carrying current will result in a?
Give the 3 ways to induce a voltage in a wire by electromagnetic induction?
1. the conduction can move through a magnetic field
2.the magnetic field can move past the conduction
3.the strength of the magnetic field can change
helix coil of wire that carries a current
Any materials which tend to oppose the flow of electrons are termed?
What devices are used for the storage of electricity?
Velocity of all electromagnetic radiation in a vacuum is?
3x10^10cm/sec or 3x10^8m/s
The resistance of a wire is related to its?
The magnetic force lines or lines of flux in a magnetic field flow?
1. within the magnet itself
2. outside the magnet
The amount of electrical potential, or potential difference in an electrical circuit, is measured by a unit called?
The electrical discharge that occurs between 2 oppositely charged objects, when the insulating properties of the transfer medium is exceeded is called?
Si unit for magnetic field strength is?
An electromagnetic device consists of a single iron core surrounded by a wire carrying current is?
The type of electricity associated w/the flow of current in a single direction is termed?
A hydrogen atom, orbital electron, & Iron atom are all associated w/ what?
magnetic moment (field)
A circuit which has 6.3x 10^18 electrons flowing per sec is said to have a current of/
The power of a circuit is equal to the product of current & voltage & is measured by what unit?
The resistance of a wire will increase as what increases?
The force within an electric circuit most responsible for the movement of current is termed?
The magnetic dipole resulting from the proton spin in a hydrogen nucleus is termed?
The laws of magnetism are similar to the laws of electrostatic bc they both?
are produced by the same physical process
The frequency (hertz) of an electromagnetic wave is best defined as?
number of oscillations or cycles per sec
In a solid conductor, current consists of a flow of moving?
A commonly used device used in the detection of a magnetic field is?
magnetic field lines
The electrical resistance which occurs in a conductor is most often manifested as the amount of _______ created?
Have the ability to deflect the path of an electromagnetic photon beam?
strong gravitational field
n a magnet the individual magnetic domains are aligned in?
The principle of electromagnetic induction is based upon experiments show that whenever a conductor cuts across magnetic flux?
an EMF is induced
Electrification may occur from what processes?
The total current through each resistor is the same for all parts of the series circuit? T or F?
Magnetic fields are a phenomenon associated with?
Heta is a form of electromagnetic radiation produced at relatively low energies called?
What units are used to measure the magnetic flux density?
Tesla or gauss
Give an example of an artificial permanent magnet?
bar magnet, compass
The strong magnetic dipole of a hydrogen atom is due in large part to?
unpaired orbital electron
Which members of the electromagnetic spectrum will normally have photon wavelengths longer than those of diagnostic xray photons?
Which type of radiation possesses sufficient energies to cause ionization?
The production of electricity by the rotation of a coil of wire within a stationary magnetic field is termed?
What is true of both 100keV x-rays & 10 keV gamma ray?
they have 0 mass
The transfer of same charge to an uncharged object by placing the 2 objects in contact with eachother is termed?
Amplitude of a sine wave is its?
min to max
The frequency of a sine wave is?
number of valleys that pass per second (# of wavelengths per sec)
Electromagnetic radiation exists at?
the speed of light or not at all (3x10^8 m/s)
Inverse square law is a result of?
The equivalence of mass & energy is described by?
the magnetic field of a single electron
Which will induce an EMF of the greatest magnitude?
A) conductor cutting flux @ 45 degree angle
B) conductor cutting flux @ a 90 degrees angle
Conductor cutting flux @ a 90 degree angle
A ____ ______ always surrounds a conductor in which a current is flowing?
A magnet's electrons spin predominantly in ______ directions?
State(2) of the 3 laws of magnetism?
1. like poles repel, opposites attract
2.every magnet has a N & S pole
3.the farther apart the magnets are the weeker the field strength
The principle difference between an xray photon & a gamma ray is?
region in the atom from where the photon originates
Sunburn is common reaction to overexposure to a normal component of sunlight called?
Partial absorption of energy by any form of matter is?
Energy of an electromagnetic radiation is directly proportional to?
frequency of the radiation
Xray wavelength has what type of relationship w/ frequency?
A single unit of electromagnetic radiation is also called?
What has a constant value for all electromagnetic radiation?
Velocity of light is?
3x10^10 cm/s (3x10^8 meters or speed of light)
The principal difference between xrays & gamma rays is their?
Give example of a natural magnet?
If a metal is easy to magnetize, it will be _____ to demagnetize?
Magnetic lines of force exit the ______ pole, curve around the surrounding space & are directed towards the ____ pole?
Glass, when placed in a magnetic field, will distort the lines of flux? T or F?
The two types of electrical charges are derived from their corresponding charged atomic particles called?
electrons & protons
The rubbing of fur & amber or silk w/glass result in electrification by a process called?
According to the 1st law of electrostatics, 2 objects with opposite charges will tend to?
An object with a net positive charge can be described as having a deficiency of?
A major source of electrical current which is produced by a chemical process is a?
Give examples of a natural magnet?
Which of the following is true concerning the energy of electromagnetic radiation?
the energy of a wave will increase as its frequency increases
All electromagnetic radiations produce a type of variation in space known as?
Member of the electromagnetic spectrum possessing a wavelength of 700 nanometers is?
The wave equation is described as?
wavelength is velocity divided by frequency
The law which relates to the relative amperage, voltage & resistance in a direct current circuit is?
The dual wave & particle natures of electromagnetic radiation was 1st proposed by?
many atoms aligned to produce a larger magnetic field
a magnets ability to resist demagnetization
Magnetism is the ability of a material to attract _______, ______, and _______?
Iron,cobalt, & nickel
the ease with which a material can be magnetized
Give examples of materials with a high electrical resistance?
An electromagnetic device which converts mechanical into electrical energy is termed?
The electrostatic force between 2 charged objects is ________ proportional to the product of their magnitudes?
Give examples of electrical conductors?
According to the principle stated in coulombs law, the electrostatic force between 2 charged objects is _____ proportional to the ______ of the distance between them?
The electromagnetic spectrum contains what & scales?
Properties of electromagnetic energy photons include?
3 wave parameters?
Frequency range of electromagnetic energy is?
one of the 4 basic forces in the universe
Frequency is? Measured in?
the wave's rate, Hertz(Hz)
x-rays traveling all the way through
Photons have what?
magnetic & electrical fields that continuously change
SI unit of charge?
Electric charges come in units that are?
positive or negative
Electromagnetic spectrum extends from what to what?
approximately 10^2 to 10^24 Hz
Electrification can be created by?
Electrification by friction occurs by?
rubbing electrons off one object &depositing them on another
When the charged body confers the opposite kind of charge on the metallic body this is known as?
The ease at which a material can be penetrated by a magnetic field?
Unit for electrical charge is?
When iron is fabricated into a magnet the magnetic domains do what?
When iron is brought near a permanent magnet, the lines of the magnetic field are?
attracted to the iron
2 types of waves?
2. longitudinal (compressional)
Electrical continuum is?
an uninterrupted ordered sequence
What happens to amplitude as waves spread out?
it drops; they lose height as they spread
Sound waves amplitude translates into?
volume & loudness
What is amplitude for sound wave?
maximum displacement of molecules in a compression or in an expansion from where they would be if the air were undisturbed
One (Hz) Hertz is equal to?
1 cycle per sec
Photons have no?
What is the speed of speed of light?
Electromagnetic energy exists in a larger range called?
In xrays amplitude relates to?
intensity of the beam
Amplitude is what?
max distance of a single trough or crest from the undisturbed water level
Velocity is? Measured in?
Speed of wave; meters per sec
Wavelength is? Measured in?
length of wave; meters
The decrease in intensity is ______ proportional to the square of the distance of the object from the source?
Various types of energy on the electromagnetic spectrum are similar how? How are they different?
Same photons; frequency & wavelength
Xrays are identified by? Measured in?
Intensity of beam; electron volts
Magnetic & electrical field are _______ to eachother?
Any electrically charged particle which is moving generates what? Along with?
magnetic field; electrical field
3 parameters of sine wave are?
One completion of the wave b4 it repeats itself?
Primary function of an xray imaging system is?
convert electric energy into electromagnetic energy
SI unit of magnetic field strength? An older unit is?
Magnetic classifications of matter are?
Accumulation of many atomic magnets w/their dipoles aligned creates?
Small magnet created by the electron orbit is called?
2 ways to get higher frequency?
traveling at faster speeds
Xray energies range from what to what?
4 measurable qualities all waves have?
study of stationary electric charges
Frequency of a series of waves will depend upon what? why?
speed of the waves & wavelengths
they are all interrelated
Magnetic field is proportional to the product of?
magnetic poles strengths divided by the square of the distance between them
Velocity of the waves will always equal?
the product of their frequency x their wavelengths
Special quantities? Def. & examples?
supports measurement in specialized areas of science & tech
Anything that has shape of form & occupies space
substance in which atoms of different elements are chemically bound together
Derived quantities are? Def. & examples?
Derived from one or more of the 3 base quantities
~composed of identical atoms that react the same way chemically
~Has "hooks" & "eyes"
Atomic mass # is what? What letter represents it?
*Always a whole number*
number of photons plus neutrons
Base quantities are? Give Def. & examples?
standard unit of measurement
A neutral atom that loses an electron by ionization is?
Photons produced during the orbital transitions of electrons from higher to lower energy are termed?
Formation of molecules can be accomplished through the interaction of valence electrons by a process called?
Ionic bonding (giving away)
Covalent bonding (sharing)
Which state of matter cprresponds to the highest degree of molecular attraction?
Most chemically stable elements having a filled outer shell configuration are termed?
Atoms with different types of nuclear configurations are?
Who discovered xrays? When?
Wilhelm Conrad Roentgen
amount of matter; not its weight
After alpha decay, the atomic # of the parent nuclide will?
Decreases by 2
combo of 2 or more sub in such a way that are not chemically bound together
After beta decay the number of a daughter nuclide?
Increases by 1
Write particles & their charges & know which has the greatest mass to the least amount?
1. neutrons: most mass- no charge
2.Proton: more mass teh an electron but less mass then a neutron- positive charge
3.Electron: least amount of mass- negative charge
Examples of electromagnetic energy?
What is Albert Einsteins theory of relativity?
matter & energy are interchangeable
Is velocity a derived or base quantity?
Penetrating distances in order from which can go the shortest distance to farthest?
gamma & x-ray
Any atom which is radioactive?
Any atom which is radioactive bc it has too few or too many neutrons?
Newton's 1st Law
A body will remain @ rest or continue moving with constant velocity if unless acted on by an outside force
Atomic number is? Represented by?
number of protons
the letter Z
What is the period number?
Number of shells
Group number is?
number of e's in the outer shell
Work & energy are both measured in the SI units called?
Max # of electron shells an atom may have?
Process of removing or adding an electron to an atom?
Smallest particle of an element, has all the characteristic properties of that element?
Chemical properties of an atom are primarily controlled by?
Principle force involved with nuclear binding is?
any time 2 or more atoms are chemically bound together
Rate of radioactive decay is greatly influenced by?
Independent all forces
Newton's 3rd Law
for every action there is an equal and opposite reaction
Which particle consists of 2 neutrons & 2 protons bound together?
How is a compound formed?
Ionic or covalent interaction
Most likely radionuclides undergoing spontaneous beta decay will possess an infavorably high N/Z ratio with an excess of?
The force that acts on an object is equal to the mass of the object multiplied by the acceleration produced?
Newtons 2nd Law (law of motion)
Force is measured in the SI unit of?
Smallest subdivision of a compound that has the characteristic properties of that compound?
energy of motion @ molecular level
directly related to temperature
Def. of electromagnetic energy?
waves of elecricity & magnetic energy moving together through space
contains a positively charged nucleus surrounded by negatively charged electrons in fixed orbits
Greeks thought all atoms were composed of?
Created the periodic table?
Schematic display after employed to represent the structure of the atom was developed by?
SI unit for mass?
no mass & no charge
Z plus N
Who said "entities must not be multiplied beyond what is necessary" what is this known as?
William of Ockham
Standard unit of time?
in power distribution is identified by the:
passing through the step-up transformer, the electrical current waveform is:
For the purpose of inducing thermionic emission, the current supplied to the x-ray
tube filament is:_______current; ______ voltage
High Current; Low Voltage
In the basic x-ray machine circuit, the last electronic device through which
high-voltage electricity must pass before reaching the x-ray tube is always the:
The x-ray tube envelope is composed
of a heat resistant material called?
pyrex glass (could be metal also)
The milliamperage stations are activated, heating up
the filament and boiling off electrons inthe x-ray tube each time you:
a. turn on the machine
b. engage the rotor switch
c. engage the exposure switch
d. release the exposure switch
Engage the rotor switch
What is the voltage waveform for the x-ray tube current passing from cathode to
anode during an exposure:
In an induction motor, an electrical current is induced in:
Only the rotor
Which part of the x-ray tube is made of thorium-impregnated tungsten:
An x-ray machine with three rectifiers would best be described as:
Which area would be defined as the area of heat dispersion on the x-ray tube anode (e.g. where does the electrons hit the anode):
In comparing three-phase x-ray generators to single-phase generators, the
three-phase generators produce:
a. higher ripple effect
b. higher subject contrast in the remnant
c. higher effective mA
d. lower effective kV
Higher effective mA
When the exposure switch is engaged, which circuit
is used to apply current to the filament in the x-ray tube?
The difference in charge between the cathode and anode during an x-ray exposure is
The maximum number of pulses of electricity that can be produced by a single-phase
x-ray generator is per second:
The formula, 0.7 X mA X kVp / 1000 gives us the:
power rating for a single-phase generator
Tungsten is the principle material used in the:
Anode disk and Filament
The autotransformer has ____ winding(s).
The step-up transformer increases
voltage _____ times
The difference between the sine wave seen on primary vs. secondary sides of the
high voltage transformer is the _____.
The material often added to a rotating anode disc to reduce surface defects and
improve rotational balance is:
The efficiency and life span of the filament wire is improved by the addition of:
What is the portion
of the induction motor that operates within the vacuum of
the enclosed x-ray tube?
A single-phase waveform has _____ ripple.
As an x-ray tube ages, the inside
can become coated with tungsten which can cause?
High capacity tube rotors revolve at a maximum ____ rpm.
The filament in an x-ray tube is about _____ length.
The effective focal spot size is _____ the actual spot size.
(e.g. smaller, larger, the same size).
The heel effect is caused by:
A line voltage compensator is incorporated into the primary circuit of a modern radiograph unit to?
maintain a constant KVp level
The type of meter that is used to measure the current passing between the electrodes of an x-ray tube?
A transformer has 60 primary and 12000 secondary turns of wire. How much voltage will be induced on to the secondary side if a 400-volt primary power supply is impressed on the device?
The voltage in the secondary circuit of a modern x-ray circuit is normally about ________ than the voltage in the primary circuit?
1000 times higher
The high-tension portion of a modern x-ray circuit does NOT contain which of the following components?
the filament selector
The use of oil within the sealed housing of the xray tube is provided to?
increase the thermal cooling of the tube envelope & provide electrical insulation of the tube
Which of the following changes would be associated with a higher amount of current passing through the filament of the xray tube?
the selection of a higher mA station
The high tension (step-up) transformer of a modern x-ray circuit is most closely related to?
the high potential required to accelerate the electrons across the tube
Which components are likely foud in the primary circuit of a mdern x-ray unit?
The high temperatures that are needed to produce the thermionic emmision in the filament of an x-ray tube require a current of about?
the majority of components in a modern x-ray circuit are found in the primary circuit. This is done to?
reduce the risk from electrical shock
The current passing between the secondary of the high tension transformer and the rectifiers is best described as a type of?
High voltage (KV) AC
In nearly all modern units the use of the large focal is initiated when the exposure setting above ______ is employed?
Most xray machines used in the United States are designed to operate on a 220 volt or 440 volt?
60 hertz, alternating current power supply
Which current regulating devices are required in the production of the high-voltage direct current needed in the xray production process?
The control of the amount of filament current in most modern radiographic units are directly related to the?
IN nearly all-radiographic units, the high-tension transformer is located in an oil-filled tank that also houses?
In order to maintain a constant filament current as changes are made in the kilovoltage requires the use of a?
space charge compensator
The milliamperage that is impressed across the x-ray tube will have a substantial effect on the?
rate of photon production
In the filament branch of the primary circuit, the type of meter employed to measure this current is?
The purpose of a ballistic-type milliampere-second meter is to measure current flow when?
rapid exposure time setting and employed
The main component of a line voltage compensator is a device that is capable of storing small amounts of electrical charge called?
The selection of voltage to the primary of the high-tension transformerin a 3-phase unit is made by?
In order to operate properly x-ray tube requires direct electrical connections to the?
The midpoint of the high-tension transformer in a modern xray circuit is grounded. This serves to reduce?
amount of cable insulation
The selection of voltage to the high-tension transformer is most commonly made by adjusting the settings on the?
The pre-reading kv meter is incorporated into the xray control panel to measure the potential difference on the?
secondary side of the high tension transformer
Which component is NOT generally located in the high voltage portion of a modern xray circuit?
Circuit overloads occuring in the sensitive components of an electrical circuit can be prevented by the use of which of the following devices?
What is usually found on the operating console of a x-ray machine?
mA control switch
timer control switch
What can be used for the storage of electrical charge?
The most common device used to create the high potential difference (kilovoltage) across the xray tube is the high tension?
The reduction of voltage and development of high amperage by a step-down transformer occurs in the?
filament portion of the circuit
In the radiographic unit, the milliammeter will register only during the activation of the?
second (exposure) stage of the exposure switch
A transformer has 2000 primary and 200 secondary turns of wire. How much voltage will be induced onto the secondary side if a 200 volt primary power supply is impressed on the device?
110, 220 or 440 volts
What is contained in a typical high-voltage generator?
A change in the voltage waveform from the primary side to the secondary side of the high-voltage transformer produces a change in?
In half-wave rectification, each inverse half-cycle in the primary circuit corresponds to how many voltage pulses across the xray tube?
Which is higher for a single-phase high-voltage generator than for a 3phase high-voltage generator?
What is a disadvantage of three-phase power compared with single-phase power?
higher capital cost
Disadvantage of a self-rectified circuit is?
its limited exposure time
An exposure of 1/10s?
produces twice as much radiation if full-wave rectified than if half-wave-rectified
requires at least four rectifiers
can be a semiconductor
concerning the transformers used in the xray circuit?
the high-voltage transformer is a step-up device
What is an advantage of three-phase power over single-phase power?
increased xray intensity per mAs
Oil is used in the high-voltage section of an xray imaging system for which of the following functions?
Which power supply should provide the highest quality xray beam?
Full-wave rectified power has what voltage ripple?
Half-wave rectified power has what voltage ripple?
High-frequency power has what voltage ripple?
Three-phase, six-pulse power has what voltage ripple?
Three-phase, 12 pulse power has what voltage ripple?
2 main electrical requirements of an Xray tube?
a filamnet current of a few amps
a voltage between the filament and the anode of 1000 volts
An xray generator converts ________ energy into ________ energy?
The part of the xray generator that supplies the high voltage necessary between the cathode and the anode is called the __________ circuit?
The part of the xray generator that supplies current and voltage to the cathode of the xray tube is called the ______ circuit?
The main power line in a hospital is usually a ______ volt, _______ hertz A.C. source?
Each of the hot wires in the main power lines varies up to _____ volts positive or negative, with respect to the neutral wire?
The turns ratio of an __________ can be varied by selecting the number of turns between connections on a single coil?
The voltage on the secondary side of the autotransformer shown below will be ________ when the selector is at position 2 than when it is at position5?
To raise the voltage higher than the autotransformer is capable of raising it, a ________ transformer is included in the tube circuit?
The autotransformer is connected to the ________ side of the step-up transformer?
If a step-up transformer has a turns ratio of 500 to 1 and a voltage of 220 volts exists on the primary side, then a voltage of ________ volts will exist on the secondary side?
An xray tube operates most efficiently with ______ but the autotransformer and step-up transformer requir ______?
D.C. ; A.C.
The circuit component that changes A.C. to D.C. is called a?
A ______ is a device that allows current to flow in one direction only?
The two types of diodes are?
Electrons will flow through the diode shown below from _______ to ______?
left to right
In a modern xray circuit, the rectification of high voltage alternating current into pulsating direct current occurs between the secondary of the high tension transformer and the?
IN a 3 phase, 6 pulse rectified unit how many voltage peaks are produced for each cycle of incoming line voltage?
What is the advantage of a 3 phase power supply in a modern radiographic unit?
reduced scatter production
the principle material that is used in the formulation of a solid state diode is?
In a 3 phase radiographic unit, if one of the rectifiers is damaged prior to a radiographic exposure, which of the following is likely to occur?
a reduced amount of optical density due to a decreased radiation output
A radiographic exposure is taken on a 3-phase , 6 pulse unit, In order to maintain the same optical density using a full wave unit would require?
a doubling of mAs value
The process by which alternating current is converted into pusating direct current is termed?
IN a 3-phase, 12 pulse unit, rectificaion is accomplished by employing?
12 solid state diodes
A full-rectified waveform is represented by number?
3 phase alternating current waveform, is represented by number?
The curve represented by #5 is best described as a/an?
steady direct current curve
What #s represent direct current waveforms?
2,3, & 5 only
The main advantage of the 3-phase, over single-phase (full wave) current, is that in 3-phase current, the voltage?
never drops to a zero voltage
The type of unit most likely to possess the smallest voltage ripple is a?
3-phase, 6-pulse unit
The most common type of rectifier for use in 3-phase radiographic equipment is the ?
solid state diode
Rectification is used to suppress the inverse voltage associated with alternating current before it reaches the xray tube. This helps to?
prevent the flow of electrons towards the filament
An exposure is made on a full-wave rectified unit. In order to maintain the same optical density for an exposure made with a 3-phase, 6-pulse radiographic unit, the mAs value employed should be decreased about?
With an alternating current source the electron flow will alternate ?
120 times a second
A 3-phase, 6-pulse unit has an effective kv of about ______ is considered normal?
A satisfactory radiograph is produced using a 3-phase, 6 pulse unit. If the same technical factors are used on a single-phase unit, the radiograph would show a?
lower optical density
During the operation of an xray tube being supplied by full-wave rectified current during 50 millisecond exposure, the tube electrodes will change (reverse) polarity?
no change in polarity occurs
The most common method for obtaining a fully rectified tube current involves the use of?
Compared to single-phase xray unit, a 3-phase unit using the same technical factors will create?
more xray photons
more anode heat units
higher energy photons
The use of 3-phase, radiographic units, has the advantage of ________ when compared to single-phase units?
higher milliamperage settings
What is the power rating for a unit energized at 800 mA, 100 millisecond and 100 kVp?
3-phase current consists of three-phase voltage waveforms separated by?
Solid-state rectifiers as compared to thermionic diode have/are?
a longer life
In modern xray equipment, the device most often used for current rectification is a/an?
solid state diode
Which of the following types of single-phase radiographic units will permit the greatest instantaneous loading capacity?
full wave rectified current
The small variation of the voltage waveform of 3- phase rectified current is termed the?
In an xray tube, electrons are produced at the negative electrode or _______ and accelerated toward the positive electrode or _________?
cathode ; anode
Bc electrons are negatively charged, they are ______ the anode and ________ the cathode?
attracted ; repelled by
The process in which electrons are boiled off the filament is called?
The electrons that have been boiled off the filament are attracted to the _______?
The small area within which a beam of electrons strikes the anode is called the?
2 reasons why the element tungsten is the main ingredient of an anode?
high atomic #(74); helps to produce more bremsstrahlung
high melting point
One purpose of the glass covering that surrounds the xray tube components is to form a vacuum between the anode and cathode. Why is it desirable to minimize the amount of air in an xray tube?
If air molecules are present, the e` strike them and lose some of their KE.
The xray tube is enclosed in lead to prevent?
The size of the focal spot as seen from the pt's point of view or as received by an image receptor is called the _______ focal spot?
Bc the anode is angled somewhat, the actual focal spot _______ than the apparent focal spot?
2 purposes for using an angled anode as shown in the above drawing?
It allows heat to be spread over a larger area on the anode
A small effective focal spot ensures a better quality radiograph
To cover the range of imaging needs from low to high mA values while maintaining as small a focal spot as possible, most general purpose diagnostic x-ray tubes have ____(____) filaments?
2 problems that occur if you attempted to force a tube current of 350 mA through a small filament?
filament might overheat
focal spot might be so small that excessive amounts of heat could build up in a small area of the anode
Some generally accepted values of kVp, mA,and time for standard radiological studies are listed on a _____ chart?
A _____ chart shows how much heat is deposited in the anode when various kVp, mA, and time combinations are used?