RAD 1065 Principles of Radiographic Imaging: Chapter 4 Electromagnetism (Carlton)

orbital magnet moment

when a charged particle is in motion, a magnetic force field perpendicular to the motion will be created

spin magnetic moment

a magnetic effect created by the electrons spinning on their axes-motion creates magnetism

magnetic dipoles

groups of atoms with a net magnetic field moving in the same direction; also known as magnetic domains

magnetic domains

groups of atoms with a net magnetic field moving in the same direction; also known as magnetic domains

magnet

an object that exhibits a uniformly strong magnetic field

lines of force/lines of flux/magnetic field

the force fields that are created when magnetic dipoles orient to create a magnet

flux density

determined by field strength and the arc in which the lines of flux are located

weber (Wb)

SI unit used to measure magnetic flux

gauss (G)

the unit used for measuring magnetic flux density

natural magnets

created when iron oxide remains in the earths magnetic field for ages, slowly orienting the magnetic dipoles in the same direction; these magnets are called lodestones

artificial permanent magnets

manufactured from a steel alloy called alnico, composed of aluminum, nickel, and cobalt; while it is hot, alnico is subjected to the field of a strong commercial magnet to permit easier orientation of the magnetic dipoles-upon cooling, the magnetic filed becomes relatively permanent

electromagnets

temporary magnets produced by moving electric current; moving electrons comprise the flow of current create magnetic fields exactly in the same manner as do the orbiting and spinning atomic electrons, any flow of current produces a magnetic field; when the current ceases flowing, the magnetic field collapses

permeability

the ease with which a material can be magnetized; inversely proportional to retentivity

retentivity

the ability of a material to stay magnetized; inversely proportional to permeability

ferromagnetic

magnetic materials such as iron, cobalt, and nickel are highly permeable and greatly susceptible to induction, majority of dipoles are lying in the same direction, thus setting a natural magnetic field

paramagnetic

materials such as platinum and aluminum have low permeability and weak attraction to magnetic fields; only have a slight majority of dipoles in the same direction; ex-MRI contrast media

diamagnetic

materials such as beryllium, bismuth, and lead, are actually weakly repelled by all magnetic fields, including both north and south poles; example: water

nonmagnetic

materials such as wood, glass, and plastic that are not affected by magnetic fields and cannot be magnetized

flemmings hand rules

a series of easily remembered aids to help with the relationship between electricity and magnetism created by John Flemming

electromagnetic relays

used to protect radiographers from electrical shock by isolating control buttons on the x-ray console from the actual circuit in which high voltage is flowing

solenoid

a coil consisting of a series of loops which serve to increase flux density; often used as detent locks on the overhead crane of X-ray tubes

mutual induction

occurs when two coils are placed in proximity and a varying current supplied to the first coil induces a similar flow in the second coil

primary coil

in mutual induction, the coil that is supplied with current-this current alternates

secondary coil

in mutual induction, the coil in which the current is inducted; flow occurs in this coil

self induction

the ability of an alternating current to switch directions, causing an opposing potential difference to induce against the incoming supply of electrons; allows direct current to flow while at the same time hindering alternating current

inductive reactance

ability of an alternating current to switch directions, causing the opposing potential difference to induce against the incoming supply of electrons; measured in ohms of resistance

armature

a coil of wire that acts as a conductor

generator

a device that converts mechanical energy into electrical energy using moving lines of flux in relationship to a conductor to induce current; also known as a dynamo

slip rings

a device with attached brushes that allows the circuit to remain stationary while the armature rotates without breaking the electrical contact between them

brushes

a device attached to slip rings, that allows the circuit to remain stationary while the armature rotates without breaking the electrical contact between them

motor

a device that is supplied with electrical current to produce mechanical motion

galvanometers

used to measure direct current when permanent magnet is used

dynamometers

used to measure alternating current when electromagnets are used

ammeter

a device used to measure current connected in a series; measured in amperes

transformer

a device in which two coils are placed near one another without electrical connection; the number of turns in the coils differs, causing a change in current in the secondary coil; this serves to either increase or decrease the voltage

step up transformer

a device used to increase the voltage from the primary to the secondary coil

step down transformer

a device used to decrease the voltage from the primary to secondary coil

transformer law

when the voltage is increased from primary to secondary it is called a step-up transformer; when the voltage is decreased from primary to secondary it is called a step-down transformer, expressed as

I2R loss

results from the inherent resistance to current flow that is found in all conductors; power lost from resistance is proportional to the square of current; some times called copper loss

hysteresis loss

results from energy expended as the continually changing AC current magnetizes, demagnetizes, and demagnetizes the core material; also called lagging loss

coercivity

energy that causes reorientation of the magnetic dipoles

eddy current loss

result of currents opposing the cause that produced them

air-core transformer

arrangement of two coils of wire in proximity to facilitate induction

open-core transformer

arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction

closed-core transformer

arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction that converges the inside and outside the lines of force through the core

shell-type transformer

arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction

autotransformer

transformer that automatically sets by adjustments

capacitor

device capable of accumulating and storing an electrical charge

dielectric

insulation between two plates in a capacitator

farad (f)

unit of capacitance

diode

a rectifying semiconductor made by sandwiching p-type crystal with an n-type to form a p-n junction

rectification

process by which alternating current is changed to pulsating direct current

thyristor/silicon-controlled rectifier

a complex semiconductor useful for high-speed switching of primary high voltage x-ray circuit; also known as a silicon-controlled rectifier

thermionic emission

ejection of electrons from the surface of the wire due to the increased heat, causing an electron cloud; aka space charge cloud

space charge cloud

ejection of electrons from the surface of the wire due to increased heat, causing an electron cloud; aka thermionic emission

half-wave rectification

suppressed rectification resulting from only half of the incoming alternating current being converted to pulsating direct current; aka self rectification

self-rectification

suppressed rectification resulting from only half of the incoming alternating current being converting to pulsating direct current; aka half wave rectification

full-wave rectification

the conversion of the opposing half of the incoming electron flow to always move in the same direction, instead of discarding half the cycle