Physics - Chapter 4

X-ray Circuit

The study of stationary electric charges

Electrostatics

The study of electric charges in motion —> electricity

Electrodynamics

What are electrical charges measured in?

Coulombs

1C = 6.25 × 10 ^18 electrons

5 Laws of Electrostatics

1) Like charges repel; opposites attract

2) Coulombs Law - The electrostatic force between 2 charges is directly proportional to the product of their quantities and inversely proportional to the square of the distance between them.

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

5) Only negative charges are free to move in solid conductors.

The electrostatic force between 2 charges is directly proportional to the product of their quantities and inversely proportional to the square of the distance between them.

Coulombs Law - greater charge, greater force; greater distance, lesser force

What are the 3 ways an object can be electrified?

Friction - rubbing together

Contact - touching a conductor

Induction - occurs as a result of the interaction of the electric fields around 2 objects that are not in contact with each other

The ability to do work because of a separation of charges

Electric Potential

How do electrons move?

From abundance to deficiency

The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm; the expression of the difference in electric potential between 2 points.

Volt

V = Joules divided by Coulombs

What is kVp?

The peak kilovoltage and its selection represents the highest intensity of an x-ray photon possible for that setting.

True or False: For electric current to move, an electric potential must exist

True

An expression of the flow of electrons in a conductor; measured in amperes

Current

1 coulomb flowing by a given point in 1 second; the amount of current flowing with an electric potential of 1 volt in a circuit with 1 ohm

Ampere

What are the requirements for an electric current to flow?

There must be a potential difference between 2 electrodes and a suitable medium through which it can travel

Define the 2 types of Current

Direct Current - flows in only one direction (battery)

Alternating Current - current that changes direction in cycles (electricity in homes)

Property of an element in a circuit that impedes the flow of electricity; measured in ohms

Resistance

The electrical resistance = to the resistance between 2 points along a conductor that produces a current of 1 ampere when a potential difference of 1 volt is applied

Ohms

The relationship between current and resistance is directly proportional.

False - Inverse

The potential difference (voltage) across the total circuit or any part of that circuit is = to the current (amperes) multiplied by the resistance

Ohms Law

V = IR

The amount of resistance depends on?

1) Material - some materials allow a free flow of current while others have resistance due to electrons

2) Length - Directly proportional; long conductor = more resistance

3) Cross - Sectional Area - A large cross-sectional area has a lower resistance bc there is greater external surface area on which electrons can travel

4) Temperature - Increased temperature increases resistance

An abundance of free electrons that allow a relatively free flow of electricity

Conductor - copper, gold, water

Tightly bound electrons that do not conduct electricity well; have no free electrons

Insulators, non-metallic elements - wood, plastic, rubber, ceramic, glass

Will conduct and insulate electricity

Semi-conductors - silicon, germanium, diamond

A closed pathway composed of wires and circuit elements through which electricity may flow is called an

Electric Circuit

Closed circuit

The pathway for electricity must be closed (complete) for electricity to flow (turning ON a light switch)

Open Circuit

One in which the pathway is broken; turning OFF a light switch

Circuit elements are wired along a single conductor

Series Circuit

What are the rules for a series circuit?

Total voltage = Total current x total resistance

Resistance = Sum of individual resistances

CURRENT is = throughout

Voltage - sum of individual voltages

Circuit elements that bridge or branch across a conductor

Parallel Circuit

What are the rules of a parallel circuit?

Total voltage = total current x total resistance

Total Current = sum of individual currents

VOLTAGE is = throughout

Total Resistance is inversely proportional to the sum of the reciprocals of each individual resistance

What are the 7 electrical devices of the x-ray circuit?

Battery, capacitor, diode, resistor / rheostat, protective device (fuse/circuit breaker), switch, transformer

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

Transformer

A device that opens a circuit (breaks the pathway)

Switch

A device designed to inhibit the flow of electrons; regulates the flow of electricity through that part of the circuit where it is placed

Resistor

Rheostat - an adjustable form

Produces electrons through a chemical reaction; stores an electric charge long term; provides electric potential

Battery

Temporarily stores an electric charge

Capacitor

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

Diode

Acts as an emergency device that “breaks” or opens the circuit if there is a sudden surge of electricity to the circuit or device

Protective Device - Fuse / Circuit Breaker

A section of wire that melts quickly if the circuit flow rises excessively, thus opening the circuit

Fuse

If current flow rises excessively, the internal switch is tripped (open), stopping the flow of electricity

Circuit Breaker

A process of connecting the electrical device to the Earth via a conductor; a protective measure in which any charged object can be neutralized.

Grounding

True or False: + charges take electrons from the Earth while — charges give up electrons from the Earth until neutral

True

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

Magnetism

True or False: Orbital electrons of atoms spin in predominately multiple directions

False: One direction

Lines of force in space

Flux

3 Characteristics of Flux

Lines of flux travel from South pole to North pole INSIDE the magnet; from NORTH pole to SOUTH pole OUTSIDE of the magnet

Lines of flux in the SAME direction REPEL; lines of flux in OPPOSITE directions ATTRACT

Magnetic fields are distorted by magnetic materials and are unaffected by nonmagnetic materials

3 Laws of Magnetism

Every magnet has a NORTH pole and a SOUTH pole

LIKE poles REPEL; OPPOSITES ATTRACT

The force of attraction / repulsion varies DIRECTLY with the strength of the poles and INVERSELY with the square of the distance between them.

The strength of magnetic fields are measured in

Tesla

True or False: Glass, wood and plastic are considered paramagnetic materials

False: Those are considered non-magnetic materials and are not attracted to magnetic fields at all.

What are diamagnetic materials?

Weakly repelled materials such as water, mercury and gold

Platinum, aluminum, and gadolinium are considered blank, and are weakly attracted to magnetic fields.

Paramagnetic

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

Ferromagnetic

The phenomenon of moving a conductor (copper wire) through a magnetic field induces an electric current in that conductor

Electromagnetic Induction

True or False: Increasing the strength or speed decreases the induced voltage

False: Increases

Who discovered electromagnetic induction

Michael Faraday

The induction of electricity in a secondary coil by a moving magnetic field; a “moving” magnetic field is created

Mutual Induction

A fluctuating magnetic field “cutting” back and forth through a single coil, inducing a constant secondary current that opposes the original. Used in the autotransformer of the x-ray machine

Self-induction

An induced current flows in a direction that opposes the action that induced it

Lenz’s Law

Devices that convert mechanical energy into electrical energy

Generator

Devices that convert electrical energy into mechanical energy through electromagnetic induction

Motor

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

Transformer

3 types of transformers and how the effect voltage

Step up - increases voltage

Step down - decreases voltage

Autotransformer - operates on the principle of self-induction

For transformers, the relationship between voltage and current is directly proportional

False - inverse; as voltage increases, current decreases, as voltage decreases, current increases

List the parts of the primary circuit

Main power supply, autotransformer, circuit breakers, timer circuit, primary side of step-up transformer

Name the parts of the secondary circuit

Secondary side of the step-up transformer, milliampere meter, rectifier bank, x-ray tube

Name the parts of the Filament Circuit

Rheostat, Filaments, Step-down transformer