Chapter 4 RADR

What is Electrostatics?

The study of stationary electric charges.

What is Electrodynamics?

The study of electric charges in motion.

The smallest units of charge exist with the __ and the __.

Electron, proton.

What System International unit are electric charges measured with?

Coulomb.

One coulomb is equal to what?

6.25 × 10¹⁸ electrons.

What are conductors?

They have a large number of free electrons like copper and gold.

What are insulators?

They have very few free electrons like glass and plastic.

What are the five general principles of electrostatics?

Like charges repel; unlike attract. Force is proportional to product of quantities and inversely proportional to square of distance. Charges reside only on external surfaces. Concentration is greatest at sharpest curves. Only negative charges (electrons) move in solid conductors.

Why does electrification occur and what are 3 ways that it can happen?

Occurs when gaining a net positive or negative charge; happens by friction, contact, or induction.

For electric current to move what must exist?

An electric potential.

What is Electric Potential?

The ability to do work because of a separation of charges.

What is Current?

An expression of the flow of electricity.

What is Resistance?

That property of an element in a circuit that resists or impedes the flow of electricity.

How is x-ray production achieved?

By the manipulation of electricity.

What is the unit of measure for electrical potential?

Volts.

What is the unit of measure for current?

Ampere.

Who is Volta?

Italian physicist who invented the battery, volts was named after him.

Define a volt.

The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm.

Volts is equal to what?

Joules.

What is kVp?

Kilovoltage Peak.

What does kilovoltage peak do?

Determines beam penetration, controls film image contrast, and influences digital image contrast.

Who is Andre-Marie Ampere?

French physicist who made significant contributions to electrodynamics, ampere was named after him.

Define ampere.

1 coulomb flowing by a given point in 1 second.

What happens in a vacuum tube?

Electrons tend to jump the gap between oppositely charged electrodes.

What are the 2 types of current?

Direct Current (DC) and Alternating Current (AC).

What is DC?

Direct Current that flows in only one direction.

What is an example of DC?

A battery because it moves from a negative terminal to the positive terminal.

What is AC?

Alternating Current that changes direction in cycles as the electric potential of the source changes.

What is an example of AC?

Electricity in USA homes that flows into homes and alternates at 60 cycles per second.

How is Resistance measured?

In ohms.

Define ohm.

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

What does Ohm's Law state?

Potential difference across the total circuit or any part is equal to current multiplied by resistance (V = IR).

What is a Solenoid?

A wire twisted into a coil to strengthen its magnetic field.

What is an Electromagnet?

A solenoid with an iron core inside it, making a temporary magnet powered by electricity.

What is Electromagnetic Induction?

Creating an electric current by moving a conductor through a magnetic field.

To increase the induced voltage in a magnetic field you need these 3 things:

More coils, more speed, more strength.

What four things does the amount of resistance of a particular conductor depend on?

Material, length, cross-sectional area, and temperature.

What is a Closed Circuit?

Is complete and allows for electricity to flow (turn on switch).

What is an Open Circuit?

Is broken and does not allow electricity to flow (turn off switch).

What is a Battery?

A device that produces electrons through chemical reaction, stores long-term charge, and provides electric potential.

What is a Capacitor?

Temporarily stores an electric charge.

What is a Diode?

A one-way valve device that allows electrons to flow in only one direction.

What are Fuse and Circuit Breaker?

Protective and emergency devices that break or open the circuit if there is a sudden surge of electricity.

What is a Resistor?

Inhibits the flow of electrons, precisely regulating electricity flow through that part of the circuit.

What is a Rheostat?

Simply an adjustable or variable form of resistor.

What is a Switch?

A device that opens a circuit (breaks the pathway).

What is a Transformer?

A device that can increase or decrease voltage by a predetermined amount.

What is Grounding?

A process of connecting the electrical device to the earth via a conductor.

What is Magnetism?

The ability of a material to attract iron, cobalt, or nickel.

What is the nature of magnetic materials?

The orbital electrons of their atoms spin in predominantly one direction.

What are Magnetic Dipoles?

Atoms pointing in the same direction creating tiny magnets.

What are Magnetic Domains?

A group of atoms or dipoles whose tiny magnetic effects are lined up in the same direction.

What is Flux?

A magnetic field that consists of lines of force in space.

Lines of flux travel from __ → __ inside the magnet.

S → N.

Lines of flux travel from __ → __ outside the magnet.

N → S.

Lines of flux in the same direction do what?

Repel each other.

Lines of flux in opposite direction do what?

Attract each other.

The magnetic field is measured in what SI unit?

Tesla (T).

What are Nonmagnetic materials?

Materials not attracted to magnetic fields at all: glass, wood, plastic.

What are Diamagnetic materials?

Materials weakly repelled by magnetic fields: water, mercury, gold.

What are Paramagnetic materials?

Materials weakly attracted to magnetic fields: platinum, gadolinium, aluminum.

What are Ferromagnetic materials?

Materials strongly attracted to magnetic materials: iron, cobalt, nickel.

The principle of electromagnetism was identified by whom?

Danish physicist Hans Oersted (compass).

What are the 2 forms of electromagnetic induction?

Mutual induction and self-induction.

What is Mutual Induction?

Uses 2 coils and is the induction of electricity in a secondary coil by a moving magnetic field.

What is Self-Induction?

A changing current inside a single coil creating a second current that fights against itself.

What are Electric Generators?

Devices that convert mechanical energy into electrical energy.

What is Lenz's Law?

States that induced current flows in a direction that opposes the action that induced it.

What are Electric Motors?

Devices that convert electrical energy to mechanical energy through electromagnetic induction.

What does a Step-up transformer do?

Increases voltage.

What does a Step-down transformer do?

Decreases voltage.

Change in voltage and current is an __ relationship.

Inverse.

Automatic Exposure Timer (AEC)

a device that automatically stops the exposure timer when enough radiation has reached the image receptor to produce a properly exposed image

how does AEC work?

1. passes through the patient 2. ionization chamber detects the x-rays 3. AEC stops the exposure

how does AEC adjust the length of the exposure timer?

based on the thickness and density of the patients body part

The rectifciers are made of 2 semiconducting crystals

p-type and n-type crystals

P-type crystal

abundance of electron traps

N-type crystal

has an abundance of freely moving electrons.

positive anode and negative cathode, does it conduct?

yes

negative anode and positive cathode, does it conduct?

no

Ripple

energy fluctuates from zero to the maximum voltage

Rheostat is contolled by

mA selector

Higher the mA equals?

Lower the resistance

what is the goal of the filament circuit?

literally boil electrons out of the filament wire