# Radiologic Science for Technologists - E-Book: Chapter 4 Flashcards

Electrostatatics

The study of fixed or stationary electric charge

Electrodynamics

The study of electric charges in motion

Electrification

Is the process of adding or removing electrons from a substance

Electrification can be created by

Contact

Friction

Induction

Electrostatic law # 1

Unlike charges attract; like charges repel

Electrostatic law # 2

Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them (Coulomb's Law)

Electrostatic law # 3

When an object becomes electrified, the electric charges are uniformly distributed throughout the object or on its surface

Electrostatic law # 4

The electric charge of a conductor is concentrated along the sharpest curvature of its surface

What is the 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 F=k QaQb/d square

Name a device that applies the fourth law of electrostatics

Cattle Prod

Super conductor

Is the property of some materials to exhibit no resistance below certain critical temperature. Example: Niobium, Titanium

Conductor

Is any substance through which electrons flow easily. Most metals are good electric conductors; copper, aluminum

Semiconductor

Is a material that under some conditions behaves as an insulator and in other conditions behaves as a conductor. Example: Silicone and Germanium

Insulator

Is any material that does not allow electron flow. Wood , glass, cloth , rubber, plastic

What is the relation between electric resistance and electric current

Ohm's Law. Increasing electric Resistance result in reduced electric current

Unit of voltage

Volt (V)

Unit of Current

ampere(A)

Unit of Power

Watts (W)

Define 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 x R

If a current of 2A passes through a conductor that has a resistance of 6 ohm, what is the voltage across the conductor?

V=IR

V=2A X 6 ohm =12

A kitchen toaster draws a current of 2.5 A. If the household voltage is 110V, what is the electric resistance of the toaster

V=IR

R=V/I

110V/2.5A= 44 Ohm

Formula to create the total resistance of a circuit in series

The total resistance is equal to the sum of the individual resistance RT = R1+R2+R3

The current through each circuit element is the same and is equal to the total circuit current IT=I1=I2=I3

The sum of the voltages across each circuit elements is equal to the total circuit voltage VT=V1+V2+V3

Circuit in parallel formulas

The sum pf the current through each circuit element is equal to the total circuit current IT=I1+I2+I3

The voltage across each circuit element is the same and is equal to the total circuit voltage VT=V1=V2=V3

The total resistance is the inverse of the sum of the reciprocals of each individual resistance 1/RT=1/R1+1/R2+1/R3

Example of parallel circuit

5,4,2 find the total resistance

1/RT=1/5+1/4+1/2

LDC 19/20

20/19 = 1.05

What is the difference between direct current and alternating current

Direct current the electron flow in one direction through the conductor

Alternating current the electron flow alternatively in opposite direction

Draw a graph to represent alternating and direct current

...

What is the unit of electric power

Watts (W)

Define one watt

One watt is equal to one ampere of current flowing through an electric potential of 1 volt

P= I x V

Any charged particle in motion create a

Magnetic field

The lines of magnetic fields are always

perpendicular to the motion of the particle

What is the magnetic permeability

The ability of a material to attract the lines of magnetic field intensity

Explain paramagnetic materials

Slightly attracted to a magnet. The degree of magnetism exhibited by a material is related to the number of unpaired electron in the outer shells.

(contrast materials used in MRI)

Explain diamagnetic materials

Known as non magnetic. Weakly repelled by either magnetic pole. Can't be artificially magnetized. Example water and plastic

Explain ferromagnetic materials

Strongly attracted by magnet. Can be permanently magnetized. Examples are iron, cobalt , nickel and rare earth ceramics . An alloy of aluminum, nickel and cobalt called alnico is one of the more useful magnets produced.

Explain magnetic susceptibility

The degree to which various material can be magnetized . Ion has high magnetic susceptibility

The imaginary lines of the magnetic field leave the

north pole and enter the south pole

What is the SI unit of magnetic field strength

Tesla

What was the older unit used for magnetic field strength

Gauss

1 Tesla =

10,000 gauss

Helix

...

Solenoid

A coil of wire

Electromagnet

...

Faraday's law

An electric current is inducted to flow in a circuit if some part of that circuit is a changing (moving) magnetic field

According to Faraday's law, the magnitude of the inducted current depends on four factors

Strength of the magnetic field

Speed at which the magnetic field moves

The number of turns in the conductor

Angle of the conductor to the magnetic field

Varying magnetic field intensity induced an

Electric current

What is the function of an Induction motor

Powers the rotating anode of an x- ray tube

What is the function of a transformer

Changes the intensity of alternating voltage and current

Autotransformer, step up transformer and step down transformer

Auto transformer: Self Induction

Step up transformer: Mutual Induction

Step down transformer: Mutual Induction

Advantage of a shell type transformer

Confines more on the magnet field lines of the primary winding because the secondary is wrapped around it and there are essentially two closed cores.

Transformer law

Transforms electric potential and current into higher or lower intensity

Vs/Vp=Ns/Np

Ns/Np is known as the turns ratio of the transformer

The secondary side of a transformer has 300,000 turns; the primary side has 600 turns. What is the ratio?

Ns = 300,000

Np = 600

300,000/600= 500:1

Copper loss

Energy dissipated by resistance in the wire used ,to wind a coil

Hysteresis loss

Magnetic friction in the core due to changing magnetic field

Eddy current loss

Power loss due to electric currents induced in the core