RAD103: The Nature of Electricity, Magnetism, and the X-ray Circuit

Comprehensive vocabulary flashcards covering the principles of electricity, electrostatics, electrodynamics, magnetism, electromagnetic induction, transformer laws, and the operation and components of the x-ray circuit.

Electrostatics

The study of stationary electric charges.

Coulomb

The SI unit of electrical charge; one coulomb is equal to the electrical charge of $6.25 \times 10^{18}$ electrons.

Coulomb's Law

A fundamental law of electrostatics stating that the electrostatic force between two charges is directly proportional to the product of their quantities and inversely proportional to the square of the distance between them.

Law of Electrostatic Curvature Distribution

The principle of electrostatics stating that the concentration of charges on a curved surface of a conductor is greatest where the curvature is greatest.

Electrification by Friction

The process of charging an uncharged object by rubbing it against another material, causing electrons to transfer from one object to the other.

Electrification by Contact

The process of charging an object by bringing it into direct physical contact with a charged conductor, causing electrons to discharge or transfer.

Electrification by Induction

The process by which an uncharged metallic object experiences a shift of electrons when brought into the electric field of a charged object without direct physical contact.

Electrodynamics

The study of electric charges in motion; what is commonly referred to as electricity.

Electric Potential

The ability to do work because of a separation of charges; causes electrons to flow from an area of abundance to an area of deficiency.

Volt

The potential difference that will maintain a current of $1\text{ ampere}$ in a circuit with a resistance of $1\text{ ohm}$; also defined as the ratio of work in joules to charge in coulombs ($\text{volt} = \text{joules}/\text{coulombs}$).

Ampere

The unit of electric current defined as $1\text{ coulomb}$ flowing past a given point in $1\text{ second}$, or the amount of current flowing with an electric potential of $1\text{ volt}$ in a circuit with a resistance of $1\text{ ohm}$.

Direct Current (DC)

A type of electric current in which electric charges flow in only one direction, such as that produced by batteries.

Alternating Current (AC)

A type of electric current that reverses direction in cycles as the electric potential of the source changes; in the United States, it alternates at a frequency of $60\text{ cycles per second}$ ($60\text{ Hz}$).

Ohm

The unit of electrical resistance equal to the resistance between two points along a conductor that produces a current of $1\text{ ampere}$ when a potential difference of $1\text{ volt}$ is applied.

Ohm's Law

The relationship stating that the potential difference across a circuit or part of a circuit is equal to the current multiplied by the resistance ($V = IR$).

Conductor

A material with an abundance of free electrons in its conduction band that allows a relatively free flow of electricity, such as copper, silver, or gold.

Insulator

A material composed of atoms with tightly bound electrons and virtually no free electrons that does not conduct electricity well, such as rubber, glass, wood, or plastic.

Semiconductor

A material that conducts electricity better than an insulator but not as well as a conductor, such as silicon, germanium, or diamond.

Conductor Length and Resistance

A relationship where resistance is directly proportional to conductor length; doubling the length doubles the collisions electrons experience, thereby doubling the resistance.

Cross-Sectional Area and Resistance

A relationship where electrical resistance is inversely proportional to the cross-sectional area (thickness) of a conductor; a wider wire provides more pathways for electrons, significantly lowering resistance.

Conductor Temperature and Resistance

A property of metallic conductors where resistance increases as temperature rises because higher thermal energy causes atoms to vibrate vigorously, increasing the frequency of electron collisions.

Electric Circuit

A closed pathway composed of wires and circuit elements through which electricity may flow.

Series Circuit

A circuit arrangement in which all circuit elements are wired sequentially along a single conductor.

Parallel Circuit

A circuit arrangement in which circuit elements bridge across separate branches of the conductor.

Grounding

The protective process of connecting an electrical device to the Earth via a conductor to neutralize charged objects by accepting or giving up electrons.

Capacitor

An electrical device that temporarily stores an electric charge.

Diode

A 'one-way valve' electrical device that permits electrons to flow in only one direction.

Rheostat

An adjustable or variable form of resistor used to regulate the flow of electric current through a circuit.

Magnetism

The ability of a material to attract iron, cobalt, or nickel due to the orbital electrons of its atoms spinning predominantly in one direction.

Magnetic Dipole

A tiny magnet created on the atomic level when the orbital electrons of an atom spin predominantly in one direction.

Magnetic Domain

A group of similarly aligned magnetic dipoles or 'atomic magnets' within a material.

Magnetic Flux

Lines of force in space that make up a magnetic field, traveling south to north inside the magnet and north to south outside the magnet.

Tesla (T)

The SI unit used to measure the strength of a magnetic field; medical magnetic resonance imaging (MRI) units operate in fields ranging from $0.5\text{ T}$ to $5\text{ T}$.

Diamagnetic Materials

Materials that are weakly repelled by magnetic fields, such as water, mercury, and gold.

Paramagnetic Materials

Materials that are weakly attracted to magnetic fields, such as platinum, gadolinium, and aluminum.

Ferromagnetic Materials

Materials that are strongly attracted to magnetic fields and can be magnetized, such as iron, cobalt, and nickel.

Nonmagnetic Materials

Materials that are completely unaffected by magnetic fields, such as glass, wood, and plastic.

Oersted's Discovery

The identification of the principle of electromagnetism by Danish physicist Hans Oersted, who demonstrated that an electric current in a conductor deflects a compass needle.

Solenoid

A conductor fashioned into a coil to intensify the magnetic field created by an electric current flowing through it.

Electromagnet

A solenoid with an added ferromagnetic (iron) core to further intensify the magnetic field strength.

Electromagnetic Induction

The phenomenon discovered by Michael Faraday whereby moving a conductor through a magnetic field, or placing a conductor in a moving magnetic field, induces an electric current in the conductor.

Mutual Induction

The induction of electricity in a secondary coil by the changing magnetic field produced by an alternating current flowing through an adjacent primary coil.

Self-Induction

The process whereby an expanding and collapsing magnetic field within a single coil cuts through its own turns, inducing a secondary current that opposes the original current.

Lenz's Law

The principle stating that an induced electric current always flows in a direction such that its magnetic field opposes the change in magnetic field that induced it.

Electric Generator

A device that converts mechanical energy into electrical energy by rotating a loop or coil of wire in a magnetic field.

Electric Motor

A device that converts electrical energy into mechanical energy through electromagnetic induction and magnetic field repulsion.

Transformer

A device that increases or decreases voltage and current through electromagnetic induction.

Step-Up Transformer

A transformer that increases voltage from the primary coil to the secondary coil while decreasing current, having more turns on the secondary coil than on the primary coil.

Step-Down Transformer

A transformer that decreases voltage from the primary coil to the secondary coil while increasing current, having fewer turns on the secondary coil than on the primary coil.

Transformer Law for Voltage

A direct mathematical relationship stating that the ratio of secondary to primary voltage equals the ratio of secondary to primary coil turns ($\frac{V_s}{V_p} = \frac{N_s}{N_p}$).

Transformer Law for Current

An inverse mathematical relationship stating that the ratio of secondary to primary current equals the ratio of primary to secondary coil turns ($\frac{I_s}{I_p} = \frac{N_p}{N_s}$).

Closed-Core and Shell-Type Transformers

Advanced transformer configurations that incorporate a ferromagnetic iron core to minimize magnetic flux leakage and maximize efficiency.

Autotransformer

An adjustable transformer operating on self-induction with a single coil of wire serving as both primary and secondary windings; controlled by the kVp selector on the console.

Primary Circuit

The low-voltage section of the x-ray circuit containing the main power switch, line compensator, circuit breakers, autotransformer, exposure timer circuit, and the primary winding of the step-up transformer.

Line Compensator

A device wired to the autotransformer that automatically monitors and adjusts incoming power to maintain a stable supply of precisely $220\text{ volts}$.

Synchronous Timer

An exposure timer based on a synchronous motor designed to turn a shaft at precisely $60\text{ revolutions per second}$ through reduction gears to operate on-off switches.

Electronic Timer

A highly accurate exposure timer based on the time required to charge a capacitor to a preprogrammed level through a variable resistor.

Automatic Exposure Control (AEC)

A device that terminates the x-ray exposure automatically when a predetermined quantity of radiation has passed through the patient and ionized the gas within an ionization chamber.

Ionization Chamber

A radiolucent AEC detector placed between the patient and the image receptor that creates an electrical charge proportional to the radiation reaching it.

Secondary Circuit

The high-voltage section of the x-ray circuit consisting of the secondary winding of the step-up transformer, the mA meter, the rectifier bank, and the x-ray tube (excluding filaments).

Milliampere (mA) Meter

A device wired in series in the secondary circuit to monitor the electrical current traveling through the x-ray tube during exposure.

Rectifiers

Solid-state diode devices arranged in pairs within the secondary circuit that convert alternating current (AC) to direct current (DC) to ensure electrons flow only from cathode to anode.

Voltage Ripple

The variation or fluctuation in peak voltage across an x-ray tube waveform, ranging from $100\%$ in single-phase, to $13\%$–$3.5\%$ in three-phase, and $< 1\%$ in high-frequency rectification.

Filament Circuit

The branch of the x-ray circuit containing the rheostat, step-down transformer, and cathode filaments designed to deliver high amperage to heat the filament wire.

Cathode Filaments

Tiny coils of wire located in the cathode focusing cup corresponding to the 'large focal spot' and 'small focal spot' selections on the operator console.

Thermionic Emission

The boiling off of electrons from the cathode filament caused by passing high current through the wire until it incandesces.