Bushong Ch. 4: Electricity, Magnetism, & Electromagnetism

Electrostatics

The study of fixed or stationary electric charges

Electric charges come in what units?

Discrete units that are negative or positive

What are the two smallest units of electrical charges?

proton (+) and electron(-)

Electrodynamics

the study of electric charges in motion

Electromagnetism

describes how electrons are given electric potential energy (voltage) and how electrons in motion create magnetism

What is the relationship between the electric charges associated with electrons and protons

they have the same magnitude but opposite signs (positive or negative)

Nearly all discussions of electric charge deal with ____ electric charges

negative

When is an object Electrified?

when it has too many or too few electrons

In what 3 ways can electrification be created ?

contact, friction, or induction

When does friction occur?

When two items rub and the difference in the # of electrons travel from one to the other

What is induction?

Electrical fields acting on one another without contact through their force fields

What term refers to the Earth as a huge reservoir for stray electric charges

electric ground

Why is the cause of electrification?

the movement of negative electric charges (electrons)

The universal total number of negative charges is equal to _____?

the total number of positive charges

The fundamental unit of electric charge is called______?

the coulomb (C)

1C is equal to__ x__^?

6.3x10^18

A radiographic exposure requires 100 mAs. How many electrons is this

6.3x10^17 electrons

How many laws describe electrostatics?

4

First law of electrostatics

like charges repel, unlike attract

The electric field points ______ from a positive charge and _____ from a negative.

-outward

-inward

Uncharged particle do or do not have an electrical field?

do NOT

The force of attraction bt unlike charges and the force of repulsion bt like charges is attributed to the _____ _____?

electric field AKA: electrostatic force

Second law of electrostatics, called Coulombs' Law

Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance bt them.

Electrostatic force is ____ proportional to the product of the electrostatic charges and ______ proportional to the square of the distance bt them.

-directly

-inversely

Third law of electrostatics

Electric charge distribution is uniform throughout or on the surface

Fourth law of electrostatics

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

Define Coulombs' Law

Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance bt them.

What is the unit of electric potential?

Volts

Electric potential is sometimes called?

Voltage

Volt

that potential difference that will move one amp through a resistance of one ohm

Electric current

when an electric potential is applied to a conductor so that electrons move along the wire

What is another name for electric current

electricity

Conductor

any substance (heat or electric current) through which electrons flow easily

Insulator

any material that does not allow the flow of electrons within a conductor or during heat transfer.

What makes water a good conductor

the salts and other impurities it contains

Semiconductor

a material that under some conditions behaves as an insulator and in other conditions behaves as a conductor

What are the principal semiconductor materials

silicon and germanium

T/F: At room temperature all materials resist the flow of electricity?

True

How do superconductor effect electron flow?

Allow electron flow with no resistance below a critical temperature

What are the four electric states of matter?

conductor, insulator, semiconductor, superconductor

What are the principal superconductor materials?

Niobium

Titanium

What are the principal materials of a conductor?

Copper

Aluminum

What are the principal materials of an insulator?

Rubber

Glass

Electric circuit

the path of electron flow from the generating source through the various components and back again

What three things control the flow of electrons of an electrical circuit through resistance?

1) The diameter of the wire (the smaller the wire the more resistance)

2) Length of the conductor (the longer the conductor, the grater the resistance)

3) Temperature (as temp increase, the resistance increases)

How is electric

current measured?

Amperes (A)

What is relationship of the ampere to the number of electrons flowing in the electric circuit?

it is a proportional relationship

1 ampere is equal to_____________?

1A =_____/s

an electric charge of 1 C flowing through a conductor each second

How is electric resistance measures?

in ohms (Greek omega)

Ohm's law

the voltage across the total circuit or any portion of the circuit is equal to the current times the resistance

What is the formula for Ohm's law

V=IR

(V is in volts, I is in amps, R is in ohms)

what are the variations in Ohm's Law?

I=V/R and R=V/I

What are the 2 basic types of circuits

series and parallel

Define Series Circuit:

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

What are the 3 rules for series circuits?

1) R(t)=R(1)+R(2)+R(3): the total resistance is equal to the sum of the individual resistances

2) I= I(1) = I(2) = I(3); the current through each circuit element is the same and is equal to the total circuit current

3) the sum of the voltages across each circuit element is equal to the total circuit voltage

What is the total resistance of a series circuit with resistors of 2, 4, and 6 ohms

12 ohms (Rt = R1+R2+R3)

Parallel circuit

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

Electric current

the flow of electrons through a conductor

List 5 other circuit Elements:

Fuse, Breaker, Resistor, Battery, Capacitor, Transformer, and Diode

Fuse

Prevents circuit overload; must be replaced when burnt out

Breaker

Prevents circuit overload; doesn't need replaced, only rest

Resistor

Inhibits the flow of electrons

Give an example of a variable resistor

Light switch dimmer

Battery

Provides electric potential

Capacitor

Momentarily stores electric charge

Transformer

Increases or decreases voltage by fixed amount

Diode

Allows electrons to slow in only one direction

Direct current (DC)

electricity where the electrons have been made to flow in one direction along the conductor

Alternating current (AC)

electricity where the electrons flow first in one direction and then in the opposite direction

What type of graph can describe direct and alternating currents?

Waveform graph

What is a sine wave?

The waveform alternating current (AC)

Directional flow of electrons in an AC?

First in a positive direction then in a negative direction

How often is the oscillation of electron direction of an AC occur sinusoidally?

1/60 sec

Unit of measurement for AC?

Hertz

How is electric power measured?

Watts

Watt

1 amp of current flowing thru an electric potential of 1 V

1 W = ! A

What is the equation for power (watts)

P = IV

where P is the power in watts, I is the current in amperes, and V is the electric potential in volts

What is the power rating of an x-ray generator capable of 200 mA @ 100kV?

P =IV

P = .2 amps x 100,000 V

P= 20,000 watts, or 20 kW

Define Magnetism:

The polarization of a material; it is the fundamental property of some forms of matter

What was the stone found in what is now Western Turkey that pointed the way to water when it came to rest

magnetite

What is another name for magnetite

lodestone

T/F: Any charged particle in motion will create a magnetic field?

True

The magnetic field of a charged particle is ____ to the motion of that particle

Perpendicular

How is the intensity of a magnetic field represented?

By imaginary lines

The lines of a magnetic field are always ___

closed loops

Define electron spin:

The electron rotation around an imaginary axis, clockwise or counter clockwise, that creates a magnetic field

How is the magnetic field in an electron spin neutralized?

in electron pairs

Bipolar or dipolar field

a field that always has a north and a south pole

Magnetic Dipole

A small magnet created by the electron orbit

Magnetic Domain:

An accumulation of many atomic magnets with their dipoles aligned

Explain how a magnetic domain can cause an object to behave like a magnet:

Under normal circumstances, magnetic domains are randomly distributed. When acted upon by an external magnetic field (earth, EM magnet, etc.) randomly oriented dipoles will align with the magnetic field

Magnetic permeability

the ability of a material to attract the lines of magnetic field intensity

How are magnets classified

according to the origin of the magnetic property

What are the three principle types of magnets?

1) Naturally occurring

2) Artificially - induced permanent magnets

3) Electromagnets

What is the best example of a naturally occurring magnet

the Earth

T/F: Artificially induced Permanent magnets come in many shapes and sizes?

True

How are permanent magnets made?

by aligning their domains in the field of an electromagnet

Are permanent magnets actually permanent?

no, their magnetic property can be destroyed by heating it or by hitting it, or anything that causes individual magnetic domains to be jarred from their alignment

What material are artificially induced permanent magnets usually made of?

Iron

List 5 states of matter:

1) Non-Magnetic

2)Diamagnetic material

3) Ferromagnetic Material

4) Paramagnetic Material

5) Magnetic Susceptibility