RADT 102 EXAM #2 - ELECTROMAGNETISM / ELECTRICITY / MAGNETISM

What is the PURPOSE of the x-ray unit

to convert electric energy into ELECTROMAGNETIC ENERGY of the x-ray beam

Describe ELECTRIC CIRCUITS

• electrons flow along OUTER surface of wire

• when the path is CLOSED and RESISTANCE can be controlled, it is a circuit

With ADDED resistance, the coming voltages are going to be _______ and ______ on the other side of the resistance

stronger, increased

Higher resistance = higher ______

voltage

When voltage goes up, amperage ________

goes down

When kilovolts go up, amperage _______

goes down

As DIAMETER got smaller, RESISTANCE ______ and gets more power/voltage to come out to go further

increased

Any CHARGED particle in MOTION creates a _____ ______

magnetic field

Describe the HISTORY of battery

• luigi Galvani = frog leg

• Alessandro volta = voltaic pile (battery sandwich) … the first battery

  • stacked copper and zinc together with a layer of wet paper between metals producing a weak current (electricity flowing)

Modern batteries have ….

• positive carbon rod

• surrounded by electrolytic paste

• housed in a negative zinc

• a battery is a source of conversion of some form of energy (magnetic) into electric current

• battery is a source of EMF

What is EMF

Electromotive force

• denotes and measured in VOLTS

• is the voltage developed by any source of electrical energy (like battery or dynamo)

What did HANS OERSTED do?

• discovered the relationship between magnetism and electric current

• a magnetic field is produced by CURRENT running through the wire

• any charge in motion induces a magnetic field

What is the HAND rule?

• right hand

• thumb (conductor) indicates the direction of the current

• fingers indicate direction of magnetic field lines

• they can be magnetized

If a wire is formed into LOOPS, what happens to RESISTANCE and MAGNETIC FIELD

• resistance INCREASE

• magnetic field INCREASE / GETS STRONGER

• increased turns = more coils

• increased turns = more resistance

What is the FARADAY RULE

aka the 1st law of electromagnetism

• a magnetic field cannot be still and produce a current. But if the magnet is moving a current is produced

• something has to move for the electrons to move (whether it is the wire or magnet)

On a STEP-UP TRANSFORMER, there is more VOLTAGE / COILS on the _______ side

secondary

On a STEP-DOWN TRANSFORMER, there is more VOLTAGE / COILS on the _______ side

primary

On the SECONDARY side of a STEP-DOWN TRANSFORMER, there would be _____ amperage

increased

To PRODUCE an electric current, what do you do?

• move a bar near a coil of wire

• OR

• move coil of wire near stationary magnet

• current increases with increase in magnetic field

INDUCED CURRENT by a magnet depends on what? (FARADAY RULE CONT)

• strength of magnetic field

• velocity of magnetic field

• angle of the conductor to the magnetic field

• # of turns in a ocnductor

  • more turns = higher voltage

• how fast is the movement

What is MOVING in an x-ray circuit to produce a current in the coils?

prior to rectification, the current going through the transformers in a x-ray unit is AC

• AC has pulses, which is the movement making the voltage / amperage able to move

What is the STEP-DOWN TRANSFORMER also called?

filament circuit

On which side of the TRANSFORMER does the AC go through rectification, converting to DC?

secondary side

Where is the rectification system in an x-ray schematic?

between the x-ray tube and the secondary side of step-up transformer

What is the FORMULA for VOLTAGE and turns (transformer law)

Vs / Vp = Ns / Np

• v = voltage

• s = secondary

• p = primary

• n = # of turns

For VOLTAGE, the transformer law formula has a _____ relationship

direct

What is the FORMULA for AMPERAGE and turns (transformer law)

Is / Ip = Np / Ns

• I = intensity

• s = secondary

• p = primary

• n = # of turns

For AMPERAGE, the transformer law formula has a _______ relationship

indirect

If a transformer has a ratio GREATER than 1, it is what

a step up transformer

If a transformer has a ratio LESS than 1, it is what

a step down transformer

What is LENZ’S LAW

the basis for self-induction

What in an x-ray circuit runs on self-induction?

• autotransformer

• choke coil (allows for adjustment of filament voltage)

Describe the AUTOTRANSFORMER

• one winding, iron core

• kVp selector taps off of this

• line voltage compensator taps off of this

• has primary / secondary side

• can act as both step-up and step-down

• kVp SELECTED here, not produced

The autotransformer is considered ________, while the step up / step down transformers are considered ________

self-induction, mutual conduction

What does MUTUAL CONDUCTION mean

you need more than one coil to act (like the step up / step down)

Describe the SHELL TYPE transformer

keeps the magnetism contained due to its structure of two closed cores

Describe the CLOSED-CORE transformer

two separate coils to identify step-up and step-down

What does a MOTOR do

converts ELECTRICAL energy to MECHANICAL

What does a GENERATOR do

converts MECHANICAL energy to ELECTRICAL

Matter has …

• mass

• form

• energy

• sometimes electric charge

Electric charge is primarily associated with ______, why?

electrons

• they can travel from outer shell of one atom to another easily

• protons can’t travel easily because they are fixed in the nucleus

What is STATIC ELECTRICITY

electricity that can’t be captured

• can’t capture electrons jumping from point A to point B

An object must be in what state to be considered ELECTRIFIED?

an object that has too many or too few electrons

What are the different causes of ELECTRIFICATION

• contact

  • person to object

• friction

  • balloon

• induction

  • lightning

What is an ELECTRIC GROUND

something that can accept excessive charges

• e.g. the Earth … it can act as a reservoir for stray electric charges, like lightning

• e.g. car’s tires, electrical cords

What is a COULOMB (C)

the fundamental measuring unit for electric charge (1C)

• 6.3 × 10 to the eighteenth power electron charges

List the ELECTROSTATIC LAWS

• like charges repel

• unlike charges attract

• both form an electric field

• positive field radiate outward

• negative field radiate inward

What is ELECTROSTATIC FORCE

the repulsion or attraction between charges due to the electric field

• both repulsion and attraction create fields, but ideal field is attraction

Describe COULOMB’S LAW

the GREATER the electrostatic charges for either object, the GREATER the electrostatic force

• direct relationship

• force gets stronger when objects are closer, weaker with the increase of distance

Electric charges are ______ distributed throughout the object or on its surface

uniformly

Describe ELECTRIC CHARGE CONCENTRATION

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

• wherever a curve is, the greater charge is there

What do INSULATORS do?

impede the flow of electrons

• e.g. rubber on tires of cars, stops electricity

Describe SEMICONDUCTORS

• these conductors sometimes let electrons flow through and sometimes impede the flow

• e.g. rectification

  • you can take negative and stop it and allow the positive to go through

• diode

What are the FORMULAS for OHM’S LAW (V = IR)

• V = I x R

• I = V / R

• R = V / I

  • I = amps

  • V = volts

  • R = resistance

If RESISTANCE goes up, VOLTAGE should go _____, AMPERAGE should go _____

up, down

Describe ELECTRIC POWER

P = IV

• P = wattages

• volts and amps

• systems only have certain wattage levels it can handle

What does a ROTOR do?

• spins

• 3400 rpm

Describe a ROTOR

• made out of ferramagnetic material (iron)

• around it are stators (aka electromagnetics)

  • these have electricity and are highly conductive

  • when they spin around on the rotor, they produce a magnetic field one at a time

• rotor (a magnet) tries to align to a stator and turns it, turning one off and turning the next one on

• electricity follows this created magnetic field, making it spin

Does the ROTOR get any electric current / electricity?

No

• the electromagnets around the rotor are the ones being energized

Describe ELECTRON SPIN

• electrons behave like they rotate on an axis

• this spin creates a magnetic field

Define DIPOLAR/BIPOLAR

magnet that has two poles

What is a MAGNETIC DIPOLE

a small magnet created by the electron orbit

• current that flows in an infinitesimally small loop

What is a NATURAL MAGNET

magnets that get their magnetism from the Earth

• created by external forces

• lodestone (leading stone) is a type of magnet naturally occurring

• best example is the Earth, because it has a magnetic field due to it spinning on axis

What is an ARTIFICALLY PRODUCED PERMANENT MAGNET

produced by aligning their domains in the field of an electromagnet

• e.g. a compass

• they don’t always stay permanent, they can be destroyed due to misalignment and loss of magnetism

What are ELECTROMAGNETS

coil or wire wrapped around an iron core that intensifies the magnetic field

• on x-ray circuit = primary/secondary coils of step up / step down transformers and autotransformer

Describe the term FERROMAGNETIC

material that is STRONGLY attracted by a magnet and usually can be permanently magnetized by exposure to magnetic field

• iron, cobalt, and nickel

Describe the term DIMAGNETIC

material that is UNAFFECTED when brought into magnetic field (not impacted)

Describe the term PARAMAGNETIC

material that is SLIGHTLY attracted to a magnet and loosely influenced by magnetic field

• in between ferromagnetic and diamagnetic

• e.g. contrast agents utilized in MRI

What is TESLA

the SI unit of magnetic field strength