Med Imaging 4 - Electricity + Electrostatics

Define electricity

A form of energy created by the activity of electrons and other subatomic particles in motion

Define electrostatics

Study of stationary (static) electric charges

What is the unit of electric potential?

Volt

What is the 1st law of electrostatics?

Like charges repel and unlike charges attract each other

What is the 2nd law of electrostatics?

The electrostatic force between two charges is directly proportional to the product of their quantities and inversely proportional to the square of the distance between them (Coulomb’s Law)

What is the 3rd law of electrostatics?

Electric charges reside only on the external surface of conductors

What is the 4th law of electrostatics?

The concentration of charges on a curved surface of a conductor is greatest where the curvature is greatest

What is the 5th law of electrostatics?

Only negative charges (electrons) are free to move in solid conductors (i.e. metals)

Removal of outer shell e- _____ substances from which they were removed, resulting in _______?

Electrifies, Static electricity

Shock occurs because e- rubbed off onto a surface you touched and you become _______

Electrified

An object is said to be electrified if it has ___ _____ or ___ _____ electrons

Too few, too many

Define electric ground

The Earth serves as an infinite reservoir for electrons, always available to accept electric charges from an electrified object

What are the 3 methods of electrification?

Friction, contact, induction

Friction

Occurs when one object is rubbed on another

Contact

Occurs when 2 objects touch, permits e- to move from one object to another, static discharge (lightning)

Induction

Process of electric fields acting on one another without contact, used in operation of electronic devices

What does Coulomb’s Law state?

The amount of elecrostatic force between 2 objects depends on the amount of electric charge in each (the product of their quantities) and the distance between them

The inverse square law says that the amount of light in the same area three times as far away will be _____, because light ______ _____ as it radiates from the source

1/9, spreads out

The inverse square law states that radiation intensity is:

Inversely proportional to the square of the distance

If the distance from the x-ray source is doubled, the beam intensity becomes:

One-fourth as great

If the distance from the x-ray source is cut in half, the beam intensity becomes:

Four times greater

The inverse square law in radiography applies primarily to:

Location of exposure

Increasing SID generally requires an increase in:

mAs

Define electrodynamics

Study of electrical charges in motion

Electricity does “_____” when electrons flow in an electric current through a wire from one terminal to the other

Work

Define conductor

Any substance through which electrons flow easily

What are good conductors? Which one is one of the best?

Metals, Copper

Why is water a good electric conductor?

Because of the salts and other impurities

What are the properties of electricity?

Electric Potential, Current, and Resistance

What is the unit of measure for current?

Amperage

What is the unit of measure for resistance?

Ohms

Potential energy

The ability to do work by virtue of state or position

Electric potential is the ability to do work due to ________

Separation of charges

Gravitational potential energy

The higher an object is lifted, the more potential energy it has

Electric potential energy

As the electric field is increased the greater the potential energy, the greater the elecric current once it starts flowing

Volts =

Joules/ Coulombs

What is the definition of a volt?

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

What is the SI unit for energy?

Joule

What is electric current?

The actual flow of electrons in a conductor

What are the 2 conditions that must be met for current flow?

1. There must be an electric potential difference between 2 charged objects

2. There must be a suitable medium for the electrons to travel

What are good conductors?

They contain electrons that are not tightly bound to their atom

Define ampere

The SI unit for charge per second. 1 ampere = 1 Coulomb (6.24 × 10¹⁸ charges) flowing by in 1 second

Define direct current

The current always flows out one terminal and back in the other terminal (one direction)

Alternating current

Alternates back and forth between a flow in one direction and flow in the other as the electric potential switches back and forth

Electric current behaves differently depending on the ____ in which it travels

Medium

What is the bahavior of current in gas? Ex?

Positive ions drift toward the negative electrode, negative ions drift toward the positive electrode. Neon light

What is the behavior of current in a metallic medium? What is this called?

Electrons from the conductor’s atoms move out of the valence shell to a higher energy level. The conduction band

What is an insulator? Example?

Material that prohibits the flow of electrons ; wood

What is a semiconductor? Example?

Material that acts as either a conductor or resistor ; Silicon

How are volts and amperes related?

In how they affect the strength of an electric current / Inversely

Define resistance

Material that impedes the flow of current

What does Ohm’s Law state? The formula?

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

What does resistance in a conductor depend on?

Material, Length, Cross-sectional area, Temperature

What are the 2 types of circuits?

1. Parallel

2. Series

What is the unit for electric power?

Watt

What are the protective devices found in electric currents?

Fuses, circuit breakers

Define electric charge

Property of matter that causes particles to experience a force of attraction or repulsion

Define Coulomb

SI unit of charge

Define resistor

Material that impedes the flow of electrons