Electro- dynamics and statics Exam

Mark Reynold's first big test

Materials that allow a relatively free flow of electric current

Conductors

Any substance with an abundance of free electrons will __________ electricity

conduct

T/F: aluminum, gold, and copper are good conductors

true

The property of an element that impedes the flow of electricity

resistance

The relationship b/w resistance and current

inverse- resistance goes up current goes down; resistance goes down, current goes up

Electric currents take the path of _________ resistance

least

The unit of measure for resistance

Ohm

Ohm’s Law

the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) times the resistance… V=IR

The amount of resistance depends on what 4 things?

Material

Length

Cross-sectional are

Temperature

Resistance is ____________ proportional with the length of the conductor

directly

A long conductor has ________ resistance than a short one

more

A conductor with a larger cross-sectional area will have a ____________ resistance than one with a small cross-sectional area

lower

With metallic conductors, the resistance becomes less as the temperature of the conductor ______________

lowers

Any material that does not allow electron flow

insulator

Insulators have __________ ____ free electrons

virtually no

Glass, ceramic, wood, plastic, and rubber are good examples of

insulators

material that some conditions cause it to conduct electricity and some conditions cause it to insulate electricity

semiconductor

Silicon and germanium are examples of what

semiconductors

electric potential is measured in

volts

electrons at high voltage have _____ potential energy and ________ capacity to do work

high, high

V=I?

R

V=?R

I

?=IR

V

V=IR

Ohm’s Law

V is

voltage

I is

amperes

R is

resistance

Two types of circuits?

Series

Parallel

All circuit elements are connected in a line along the same conductor?

Series circuit

Christmas lights are a good example of wat kind of circuit?

Series circuit

A circuit that contains elements that are connected at their ends rather than lying in a line along a conductor?

Parallel circuit

Current that always flows in the same direction

Direct current

Direction of the current reverses, or alternates 60 times per second (US) or 50 per second (Europe)

Alternating current

Batteries and solar cells produce what kind of current?

Direct current

Wall sockets produce what kind of current?

Alternating current

Unit of electric power

Watts

An x-ray requires ____________ of electric power?

20-150 kW

An electric circuit is the _______________ pathway of an electric current.

closed

If a circuit is broken by any means such as turning off the switch, electron flow stops. What is this called?

open circuit

A fuse is a section of __________ ________

Special wire

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

grounding

infinite reservoir of electrons

the Earth

the study of stationary electric charges

Electrostatics

the property of particles to experience force (negative or positive) in a magnetic field

electric charge

Unit of electric charge

Coulomb

What is Coulomb’s Law?

Like charges repel each other; unlike charges attract.

the amount of work needed to move a charge

electric potential

unit of electric potential

volt

A material that under certain circumstances acts as a conductor, and other circumstances acts as an insulator

semiconductor

Unit of electric current

Ampere

5 laws of electrostatics

Repulsion-attraction

inverse square law

distribution

concentration

movement

2 types of protective devices found in a circuit?

Fuse

Circuit breaker

3 main parts of the X-ray circuit

Primary Circuit

Secondary Circuit

Filament Circuit

Study of electricity of moving electric charges

electrodynamics

What are the principles of electrostatics about?

electrical charges at rest

what are the principles of electrodynamics about/

electrical charges in motion

what movement do we associate with electricity

electrodynamics: electrical charges in motion

What is electric current or electricity?

Movement of electrons through a conductor

Electricity does \____ when the electrons flow in an electric current through a wire from on terminal to the other

work

An electric current or flow of electrons occurs in a conductive metal or other substance when what exists?

an electric potential

What is a conductive substance

substance with free electrons that allow the flow of a current

what is a conductor

any substance through which electrons flow easily

True or False: Copper is one of the best conductors

true

electric potential unit of measure

voltage

current unit of measure

amperage

resistance unit of measure

ohms

kVp

kilovoltage peak

mA

milliamperes

Potential energy

the ability to do work by virtue of state or position

electric potential

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 - the more kinetic energy it will gain if it is released

True or false: Volt \= Current

False

Difference between volt and current

Volt refers to the difference in electric potential between the two charges that make the current flow. Current is the actual flow of electrons

What two conditions must be met for electric flow?

There must be an electric potential difference between the two charged objectsthere must be a suitable medium in which it can travel

Electrons flow from a \______ charge to a \____charge as long as an electric potential difference exists

negative; positive

amperes

coulombs/seconds

Amperes

the SI unit for charge per second

two types of current

direct current and alternating current

current

movement of electrons

what are the three methods of electrification

friction, contact, and induction

friction

occurs when one object is rubbed on another

contact

occurs when two objects touch - permitting electrons to move from one to another

induction

the process of electric fields acting on one another without contact

inverse square law

force between two charges is inversely proportional to the square of the distance between them

what changes alternating current to direct current in a circuit

rectifier

electrons have one unit of \____ charge

negative

protons have one unit of \____ charge

positive

positive ions

atoms with fewer electrons than protons

negative ions

atoms with more electrons than protons

the primary function of an x-ray imaging system is to convert \__ energy into _ electromagnetic energy

electric; electromagnetic

electrical charges are measured in the SI unit called __?

coulomb

one coulomb is equal to the electrical charge of ?

6.25 x 10^18

Why are electrons used for measuring electric charge rather than protons?

because their electricity is due to their movement vs. protons are fixed in their position inside the nucleus of an atom

when is an object said to be electrified

if it has too few or too many electrons