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Imaging Ch.5

Electricity, Magnetism, and Electromagnetism

TermDefinition
Electricity A form of energy created by the activity of electrons and other subatomic particles in motion.
Electrostatics The study of fixed or stationary electric charges that are at rest.
__________________ are either positive or negative. Electric charges.
Electrification The process of adding or removing electrons from a substance.
Contact Two objects actually touch permitting electrons to flow from one to another.
Friction One object is rubbed against another.
Induction The process of electrical fields acting on one another without contact.
Electrostatic Charge The smallest unit of electric charge is an electron.
Electrostatic Charge -It carries one unit of negative charge. -It is measured in coulomb.
Coulomb's law Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them (inverse square law
Repulsion-attraction Unlike charges attract, like charges repel.
Distribution When an object becomes electrified, the electric charges are uniformly distributed throughout the object or on its surface.
Concentration The electric charge of a conductor is concentrated along the sharpest curvature of its surface.
Movement Only negative charges move along solid conductors (not in text).
Electric Potential The potential of an electric charge to do work. -Sometimes called electromotive force (EMF). -Measured in Voltage.
Electrodynamics The study of electrical charges in motion -Commonly called electric current or electricity. -Measures the flow of electron.
Conductors Any substance through which electrons flow freely. Examples: electrical wire, copper, aluminum.
Superconductor A material which under certain extreme temperatures offer no resistance to electron movement.
Insulators Inhibit or prevent electrons from flowing freely. Examples are: Rubber, wood, plastic.
Semi-conductor A material that under certain conditions acts as a conductor and other conditions acts as an insulator.
Electric Circuit When resistance to electron flow is controlled and the conductor (what electrons are flowing on) is made into a closed path.
Electrical current The number of electrons flowing in the circuit. -Measured in ampere (A). -Also called Intensity (I).
Electric potential The potential number of electrons that can be used in the circuit -Measured in volts (V).
Electrical resistance Anything that hinders the movement of electrons. -Measured in ohm.
Ohm's Law The voltage across the total circuit or any portion of the circuit is equal to the current multiplied by the resistance V = I R.
Series All circuit elements are connected in a line along the same conductor.
Parallel Elements that bridge conductors rather than lie in a line along a conductor.
Direct Current Electrons flow in only one direction.
Alternating Current Electrons flow alternately in opposite directions.
Electric power Measured in watts.
Repulsion - attraction Like poles repel, unlike poles attract.
______________ of a conductor is concentrated along the sharpest curvature of the surface. Electric charge.
Increasing electric resistance results in a ___________ electrical current Reduced.
The _________ across the total circuit or any portion of the circuit is equal to the current times the resistance Voltage.
Direct Current (DC) Electrons can be made to flow in one direction along the conductor.
Alternating Current (AC) Electrons oscillate back and forth.
Any charged particle in motion creates a _______________. Magnetic field.
The ________________ of a magnetic field are always closed loops. Imaginary lines.
Magnetic permeability Is the ability of a material to attract the lines of magnetic field intensity.
The degree to which a material can be magnetized is its _______________________. Magnetic susceptibility.
All _________ can be classified according to either of four interactions with an external magnetic field. Matter.
A charge in motion includes a ________________ Magnetic field.
The ________________ of a magnetic field are always closed loops. Imaginary lines.
Magnetic permeability Is the ability of a material to attract the lines of magnetic field intensity.
The degree to which a material can be magnetized is its _____________ Magnetic susceptibility.
All _________ can be classified according to either of four interactions with an external magnetic field Matter.
____________________ objects can be made into magnets by induction. Ferromagnetic
The SI unit of magnet field strength is the ___________. Tesla.
A charge in motion includes a ________________. Magnetic field.
Solenoid A coil of wire.
Induction Motor -Composed of several external electromagnets (stator) with a fixed internal loop of wire (rotor). -Utilized in the rotor of the x-ray tube.
Electrical Motors -Converts electrical energy into mechanical energy. -Composed of the same elements as a generator except that a current is applied to the wire which creates a small magnetic field and causes the wire to move.
Direct Current Generators -Constructed similar to AC generators with the addition of a commutator ring -Commutator ring acts as a switch to reverse the negative current to positive current.
Electric Generator Converts mechanical energy to electrical energy, Composed of a loop of wire (armature) placed between 2 magnets of opposing poles,
Electric Generator Movement of the armature through the magnetic field lines causes a current to be induced in the wire, Produces Alternating Current (AC).
Mutual induction Inducing a current flow into a secondary coil by placing it in the varying magnetic field lines.
Self Induction When a current is induced due to the construction of the electromagnet.
Strength Of the magnetic field.
Speed Of the motion between the magnetic fields and the conductor.
Angle Between the magnetic fields and the conductor.
Number of turns In the conducting coil.
Faraday's Law An electric current is induced to flow in a circuit if some part of that circuit is in a changing magnetic field.
Electromagnetic A coil of wire with an iron (ferromagnetic) core.
Advantage of and Electromagnet: Magnetism can be turned on and turned off.
Oersted's Experiment -Any charge in motion induces a magnetic field. -A charge at rest produces no magnetic field.
Earliest studies of electricity: Charges could be induced to move but only in a sudden discharge.
1700 Discovery of battery (constant flow of electricity).
1820 Oersted's Experiment.
The Inverse Square Law The force between two magnetic fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them (Maxwell's Field Theory).
Magnetic poles Every magnet has two poles, a north and a south.
Ferromagnetic Highly permeable and greatly susceptible to induction.
Paramagnetic Have a low permeability and weak attraction to magnetic fields.
Diamagnetic Weakly repelled by all magnetic fields including both north and south poles.
Non-magnetic Materials that are not affected by magnetic fields and cannot be magnetized.
Electromagnets An electric wire wrapped around an iron core with an electric current flowing through it.
Artificially induced permanent magnets: A magnet that is created by charging a material in a field of an electromagnetic.
Naturally occurring magnets: The earth (loadstone).
Magnetic domain An accumulation of dipoles aligned.
Magnetic fields are always ___________________ Closed loops.
Spin Electrons spin on their axis, creating motion and a magnetic field.
Magnetite Around 1000 BC dairy farmers in the village of Magnesia discovered that certain stones possessed magnetic properties.
Lodestone They called the loadstone, or leading stone because they used it to find water.
Magnetism The word comes from that village's name.
Electromagnetic induction An electric current is induced in a circuit if some part of that circuit is in a changing magnetic field.
An ____________ motor powers that rotating anode of an x-ray tube. Induction motor.
Transformer -Transforms electric potential and current into higher and lower intensities. -Can only be used with Alternating Current.
Transformer Law As the number of turns on the primary side increases so does the voltage proportionally. Vs = Ns Vp Np
Step up transformer Steps voltage up from a lower voltage to a higher voltage -The turns ratio is greater than 1.
Step down transformer: Steps down voltage from higher to lower voltages. -The turns ratio is less than 1.
Transformer Effect on Current Current, voltage and the turns ratio is inversely proportional to one another.
Resistance For every action there is an equal but opposite reaction.
Hysteresis The additional resistance created by alternate reversal of the magnetic field caused by the AC (also called lagging loss.
Eddy currents Described by Lenz's law.
Closed core transformer -Square iron core with primary windings on one side and secondary windings on the other side. -Operates by means of mutual induction.
Autotransformer (open core) -Contains one coil of wire with an iron core which acts as primary and secondary windings. -Operates by means of self induction rather than mutual induction.
Shell Type -Composed of two closed iron cores which has one winding in the center of the two cores. -Operates by means of self induction.
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