Chapter 4 p1 - Electrostatics

alternating current (AC):

is current that changes direction in cycles as the electric potential of the source changes (the negative and positive “terminal” alternate)

automatic exposure control:

a device that uses an ionization chamber to detect the quantity of radiation exposing the patient and image receptor

conductor:

material with an abundance of free electrons allowing free flow of electricity (copper and gold)

current:

is an expression of the flow of electrons in a conductor, Ampere (mAs)

direct current (DC):

is a type of current that flows in only one direction

electric potential:

is the ability to do work because of a separation of charges, Volt (kVp)

electrodynamics:

is the study of electric charges in motion (electricity)

electromagnetic induction:

the phenomenon of inducing an electric current in that conductor by moving a conductor through a magnetic field

electromagnetism:

• the phenomenon of electricity and magnetism existing as two parts of the same basic force, electromotive force

• a magnetic field is created by a flow of electricity, and a moving magnetic field can create an electric current

electrostatics:

is the study of stationary electric charges

filament circuit:

a section of the x-ray circuit that consists of a rheostat, a step-down transformer, and the filaments

generators:

devices that convert some form of mechanical energy into electrical energy (ex; force of water through a dam)

grounding:

a process of connecting the electrical device to the Earth via a conductor (a protective measure)

insulator:

• materials with very few electrons prohibiting the flow of electricity

• poor conductors of electricity

• glass, rubber

magnetism:

the ability of a material to attract iron, cobalt, or nickel

motors:

are devices that convert electrical energy to mechanical energy through electromagnetic induction

primary circuit:

a section of the x-ray circuit that consists of the main power switch (connected to the incoming power supply), circuit breakers, the auto-transformer, the timer circuit, and the primary side of the step-up transformer

resistance:

is that property of an element in a circuit that resists or impedes the flow of electricity, (Ohm)

secondary circuit:

the section of the x-ray circuit that consists of the secondary side of the step-up transformer, the milliampere meter, a rectifier bank, and the x-ray tube (except for filaments)

transformers:

devices used to increase or decrease voltage (or current) through electromagnetic induction

A step-up transformer is one that:

increases voltage

A step-down is a transformer that:

decreases voltage

The x-ray circuit may be divided into 3 sections:

1. the primary circuit

2. the secondary circuit

3. the filament circuit

Electric charge is a property of:

matter

There are four general laws of electrostatics:

1. like charges repel and unlike charges attract

2. The charge is directly proportional, it increases as the objects move closer and decreases as the objects separate. Inversely. (Coulombs law)

3. electric charges reside only on the external surface of conductors

4. the concentration of charges on a curved surface of a conductor is greatest where the curvature is greatest (tasers)

Where are only negative charges free to move in?

in solid conductors

In electrostatics, electrification of objects occurs when they gain:

either a net positive or a net negative charge

An object may be electrified from 3 ways:

friction (rubbing of hands), by contact, or by induction

For electric current to move there must exist an:

electric potential

For electric current to move there must exist an electric potential, which is the ability to do work because of a separation of charges.

What are those charges?

• an abundance of electrons (Negative) at one end of a wire and an abundance of (Positive) charges at the other end (separation of charges)

• plug cord in outlet

When an electric potential is applied to a conductor, what does it produces?

an electric current and a magnetic field

The smallest units of charge, rest with the:

proton and the electron

By design, the x-ray tube creates:

a separation of charges

The exposure factors the radiographer selects on the control panel determines the number of:

electrons that will flow and the magnitude of their attraction to the positive side

Alessandro Volta is an Italian physicist. What did he invent?

the battery in 1799

Amount of work (in joules) that can be done per unit of charge:

volt

A volt is the ratio of:

joules to coulombs (volt = joules/coulombs)

A battery that uses 6 joules of energy to move 1 coulomb of charge is a:

6-volt battery

A volt is the potential difference that will maintain a current of:

1 ampere in a circuit with a resistance of 1 ohm

One coulomb flowing by a given point in 1 second is also know as:

• Ampere

• the amount of current flowing with an electric potential of 1 volt in a circuit with a resistance of 1 ohm

For electric current to flow, the following must be present:

• a potential difference between two electrodes

• a suitable medium through which it can travel

  • vacuum

  • metallic conductors

Metallic conductor electrons, from valence shell conduction band, can drift along external surface of conductor. T/F

TRUE