Set: Radiography Physics Ch. 4

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All 62 Terms

Term Definition
nature of magnetism any charged particle in motion will create a magnetic field, the magnetic field of a charged particle in motion is perpendicular to the motion of that particle, magnetic field lines are always loops-lines of force never intersect and they flow inside as well as ouside the magnet
orbital magnetic moment magnetic force perpendicular to the plane of motion of an electron while orbiting the nucleus of an atom
spin magnetic moment small magnet created by electron spin
lines of force, lines of flux, or magnetic field force fields that are created when magnetic dipoles orient to create a magnet, always flow from north to south outside the magnet and south to north inside the magnet
weber si unit for magnetic flux, 1(Wb)=10e8 lines of flux
tesla unit for magnetic flux density (magnetic field strength), 1(T)=1(Wb)/me2, 1(T)=10,000 guass
classification of magnets magnets can be classified according to the origin of the magnetic properties
naturally occurring magnet earth because it spins on an axis, lodestones (magnetite) consist of iron oxide
artificial permanent magnets compass, bar or horseshoe shaped magnets, magnetic property can be destroyed by heating or jarring violently, alnico-alloy of aluminum, nickel and cobalt (very strong)
electromagnets wire wrapped around an iron core, electric current is conducted through the wire, magnetic field created is directly proportional to the electric current, the higher the current the bigger the field, themporary-when current is turned off, they are no longer magnetic
magnetic laws attraction and repulsion-like poles repel, unlike pose attract, magnetic force=inverse square law, dipoles-ever magnet has two poles north and south, magnetic fields exist around magnets
tesla si unit of magnetic field strength in the tesla
magnetic induction some materials can be easily magnetized, others cannot
permeability the eas with which a material can be magnetized
retentivity the ability of a material to stay magnetized, permeability and retentivity are inversly proportional
magnetic susceptibility the degree to which various materials can be magnetized
ferromagnetic strongly attracted by magnets ex. iron-cobalt-nickel, usually can be permanently magnetized by exposure to a magnetic field, alinco=aluminum-nickel-cobalt, rare earth ceramics
paramagnetic slightly attracted to a magnet, loosely influenced by a magnetic field, platinum-aluminum-gadolinium, MRI contrast agents=gadolinium
diamagnetic materials that are slightly repelled by a magnet, beryllium-bismuth-lead
nonmagnetic aka dimagnetic, unaffected by magnetic fields, cannot be magnetized, wood-glass-plastic-rubber, most materials are nonmagnetic
battery dry cells, any device that converts some form of energy directly into electric energy is said to be a source of EMF, EMF unit is volt or joule per coulomb
dry cells carbon rod-positive electrode, electrolytiic paste-like battery acid, zinc cylindrical-negative
oersted's discovery electric current passed through a wire will create a magnetic field, any charge in motion generates a magnetic field, fleming's left hand rule
fleming's left hand rule electron flow
solenoid stacked loops of wire condutor, intensity of magnetic field increases within the coil, magnetic field can be adjusted or turned off and on by varing the current flow through the coil
solenoid strength is determined by number of loops in the wire, strength of current
electromagnetic when the coil is wrapped around a ferromagnetic core, the magnetic field lines are even more concentrated than with a solenoid, magnetic field can be adjusted or turned off and on by varying the current flow through the coil
electromagnetic strength is determined by number of loops of wire, current strength, permeability of the core
the 2 laws that govern induced current faraday' law, len's law
faraday's law an electric current will be induced to flow in a circuit if some part of that circuit is in a changing magnetic field
len's law principle for determining the direction of induced current flow, induced current flow sets up a magnetic field opposing the action that produced the orignal current
FARADAY changing magnetic fields magnet moving=coil stationary, coil moving=magnet stationary, both are stationary=current is varied in coil
FARADAY magnitude of induced current depends on STRENGTH of the magnetic field, VELOCITY of the magnetic field increase velocity=increase current, ANGLE of the conductor to the magnetic field 0-90degrees (most current will happen at right angle to flux line), NUMBER OF TURNS in the conductor
generator aka dynamo, converts mechanical energy to electrical energy
GENERATOR alternating current coil of wire (armature) moving in a magnetic field, current changes direction, electron flow is directed to the SLIP RINGS and brushes (slip rings only allow 1 way), one complete turn of the armature=one cycle of current
GENERATOR direct current coil of wire (armature) moving in a magnetic field, current changes direction, electron flow is directed to the commutor ring (only get electricity from 1 side of armuature, pulsating direct current is produced
motor converts electrical current to mechanical energy, moves electricity, uses commutator rings
MOTOR induction motor stator-(outside) pairs of stationary electromagnets supplied with multiphase current, rotor-(inside) bars of copper around an iron core
MOTOR circuit devices ammeter-connected in series, voltmeter-connected in parallel
transformers transforms electric potential and current into higher or lower values
transformer law because of alternating current constantly changes direction, it will constantly establish, collapse, re-establish, and re-collapse the surrounding magnetic field
transformer energy loss although we calculate transformer energy output as being equal to its input, in reality there is about a 5-10% loss during conversion
3 types of transformer energy loss copper losses, hysteresis(lagging loss), eddy current losses
copper losses mainly the resistance within the wires of the of the coil, using thick wire in primary winding will decrease energy loss due to heat
hysteresis (lagging loss) magnetic domains within the core are repeatedly rearranging themselves as the core is magnetized first in one direction and then the other, rearranging causes heat production in the core, reduction of loss due to hysteresis is accomplished by the use of a laminated silicon steel core
eddy current losses the alernating magnetic flux will induce swirling electrical currents within the core, these low energy currents in effect oppose the general flow of current moving through the coil, lamination of the core (dividing the core into thin layers) hinders the formation of eddy currents
types of transformers air core, open core, closed core, shell, autotransformer
autotransformer single coil on central core, allows for inclusion of a variable number turns in the primary coil
AUTOTRANSFORMER transformers in the x-ray circuit autotransformer, high voltage step-up transformer, filament step-down transformer
capacitor stores an electrical charge, unit of capacitance is the farad (f), microfarad is typically used
retification alternating current is changed to pulsating direct current
filament cathode=negative charge, source of electrons, small diameter tungsten wire=increased resistance and heat, thermionic emission, space chage cloud
thermionic emission electrons freed from the filament following introduction of current into filament
anode positive charge, relatively large matallic surface
simple vacuum tube couducts electrons in only one direction: from the cathode to the anode
rectifiers also called diode
semiconductors solid-state rectifiers
n-type doping phosphorus or arsenic is added to the silicone in small quantities, phoshprus and arsenic each have 5 outer electrons, so they're out of place when they get into the silicon lattice, the fifth electron has nothing to bond too, so it's free to move around, it makes only a very small quantitiy of the impurity to create enough free electrons to allow an electric current to flow through the silicon, n-type silicon is a good conductor, electrons have a negative charge, hence the name n-type
p-type doping boron or gallium is dopant, boron and gallium each have only 3 outer electrons, when mixed into the silicon lattice, they form "holes" in the lattice where a silicon electron has nothing to bond too, holes can conduct current, a hole happily accepts an electron from a neighbor-moving the hole ove a space, p-type silicone is a good conductor
p-n junction p & n type semiconductors are sandwiched together to form a solid-state diode, flow of electrons from n-type to holes in p-type constitutes current flow, no flow can take place from p-type holes to n-type semiconductors
half-wave rectification during cycle, current flows in two directions, when a diode is in the circuit, the neg. portion of the cycle is suppressed or deleted, pusating direct current, when the x-ray tube itself serves as the rectifier-the system is said to be self-rectified, voltage that vary from 0-max potential 60 times per second (100% voltage ripple) during half wave rectification, contains 0-2 diodes
full-wave rectification the negatie portion of the AC is converted so that the electrons are always moving in the same direction, voltage pulsations that very from 0-max potential 120 times per second (100% voltage ripple), contains at leas 4 diodes in the high voltage circuit, nearly all stationary-3 stage x-ray machines employ full wave rectification

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Terms 62
Creator mainstang
Created March 11, 2008
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Tags physics, radiography
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radiography physics notes for chapter 4.

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mainstang : Changed autotransformer → single coil on cenral core, allows for inclusion of a variable number turns in the primary coil to autotransformer → single coil on central core, allows for inclusion of a variable number turns in the primary coil
mainstang : Changed capacitors → stores an electrical charge, unit of capacitance is the farad (f), microfarad is typically used to capacitor → stores an electrical charge, unit of capacitance is the farad (f), microfarad is typically used
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Most Missed Words

  1. electromagnetic → when the coil is wrapped around a ferromagnetic core, the magnetic field lines are even more concentrated than with a solenoid, magnetic field can be adjusted or turned off and on by varying the current flow through the coil - 2 misses
  2. nature of magnetism → any charged particle in motion will create a magnetic field, the magnetic field of a charged particle in motion is perpendicular to the motion of that particle, magnetic field lines are always loops-lines of force never intersect and they flow inside as well as ouside the magnet - 1 miss
  3. orbital magnetic moment → magnetic force perpendicular to the plane of motion of an electron while orbiting the nucleus of an atom - 1 miss
  4. lines of force, lines of flux, or magnetic field → force fields that are created when magnetic dipoles orient to create a magnet, always flow from north to south outside the magnet and south to north inside the magnet - 1 miss
  5. naturally occurring magnet → earth because it spins on an axis, lodestones (magnetite) consist of iron oxide - 1 miss
  6. electromagnets → wire wrapped around an iron core, electric current is conducted through the wire, magnetic field created is directly proportional to the electric current, the higher the current the bigger the field, themporary-when current is turned off, they are no longer magnetic - 1 miss
  7. permeability → the eas with which a material can be magnetized - 1 miss