Chapter 5: Electricity, Magnetism, and Electromagnetism

electrostatics

The study of electric charges at rest

electric charge come in discrete units that are

positive or negative

smallest units of electric charge

Electron (negative)

Proton (positive)

electron has one unit of

negative charge

proton has one unit of

positive charge

electric charges associated with an electron and proton have the same

magnitude but opposite signs

electrified

An object is said to be __ if it has too few or too many electrons.

electrification can be created by

contact, friction, induction

electric ground

The object that behaves as a reservoir for stray electric charges

lightning

A sudden spark, or energy discharge, caused when electrical charges jump between parts of a cloud, between nearby clouds, or between a cloud and the ground.

the coulomb

SI unit of electric charge

1 C = 6.3 × 1018 electron charges

electrostatic charge of one electron

One coulomb (C) is equivalent to 6.3 × 10^18 electron charges.

Four electrostatic laws

1. Unlike charges attract, like charges repel

2. Coulomb's Law- Electrostatic Force Is Directly Proportional to The Product Of The Electrostatic Charge and Inversely Proportional To The Distance Between Them

3. Electrostatic Charge Distribution Is Uniform Throughout Or On The Surface

4. The Electric Charge of A Conductor Is Concentrated Along The Sharpest Curve

electrostatic force

The force between electrically charged objects (like charges repel and opposite charges attract each other).

Coulomb's Law

F=K q₁*q₂/r², magnitude of force between two charges

inverse square law

the intensity of radiation is inversely proportional to the square of the distance from the source of radiation

electric charges have what kind of energy

potential

the unit of electric potential

volt (V)

voltage

The potential difference measured in volts. The amount of work to be done to move a charge from one point to another along an electric circuit.

Volt

The unit of potential difference symbolized as V.

potential energy/unit charge, or joule/coulomb (1 V = 1 J/C)

electricity

A form of energy caused by the movement of electrons.

electrodynamics

The study of electric charges in motion

conductor

any substance through which electrons flow easily

Copper: Variable resistance

Aluminum: Obeys Ohm's Law

Requires a voltage

insulator

A material that does not allow heat or electrons to move through it easily.

semiconductor

A substance that can conduct electricity under some conditions

superconductivity

the property of some materials to exhibit no resistance below a critical temperature

electric circuit

a complete, unbroken path through which electric charges can flow

Increasing electric resistance results in a reduced electric current

electric current is measured in

Amperes (A)

ampere

proportional to the number of electron flowing in the electric circuit.

1A= 1C/s

electric resistance

a measure of how difficult it is for an electric current to flow in a material

measured in ohms (Ω)

Ohm's law

V=IR

V is the electric potential in volts, I is the electric current in amperes, and R is the electric resistance in ohms

electric current

The continuous flow of electric charges through a conductor

Direct Current (DC)

Electric current that flows in only one direction

Alternating Current (AC)

electric current that reverses its direction of flow in a regular pattern

superconductor

Niobium: No Resistance to electron flow

Titanium: No electric potential required

Must be very cold

semiconductor

Silicon: Can be conductive

Germanium: Can be resistive

Basis for Computers

insulator

Rubber: Does not permit electron flow

Glass: Extremely high resistance

Necessary with high voltage

voltage waveform

Graphical representation of voltage over time.

electric current elements

resistor

battery

capacitor

transformer

diode

Function of a resistor

inhibits flow of electrons

Function of a battery

provides electric potential

Function of a capacitor

momentarily stores electric charge

Function of a transformer

increases or decreased voltage by fixed amount (AC only)

Function of a Diode

allows electrons to flow in only one direction

electric power is measured in

Watts (W)

amount of electric power an x-ray imaging system requires

20 to 150 kW of electric power

formula for electrical power

P=IV

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

Iodestone

a piece of magnetite that has magnetic properties and attracts iron or steel

magnetism

The force of attraction or repulsion of magnetic materials

magnetic field

the charged particle such as electron in motion is perpendicular motion of that particle

electric spin

Spinning movement electrons have similar to the earth spinning on its axis.

-creates magnetic field, which is neutralized in electric pairs

-atoms with off number of electrons in any shell have very small magnetic field

magnetic moment

The strength of a magnetic field is known as the magnetic moment. Those with a weak attractive force are referred to as paramagnetic materials, while ferromagnetic materials have a strong attractive force. A diamagnetic material has electrons that are paired, and therefore does not typically have a magnetic moment. There are, however, some diamagnetic materials that have a weak magnetic field.

Lines of magnetic field are

imaginary

dipolar

Having two poles. The water molecule possesses a polarity of electrical charge with one pole being more positive and the other more negative in electrical charge.

magnetic domain

A region in which the magnetic fields of all atoms are lined up in the same direction

magnetic permeability

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

3 principle types of magnets

Naturally Occurring, Artificially Induced Permanent, and Electromagnets

natural magnet

an object that is magnetic without human influence

i.e. Earth

artificial permanent magnets

artificially magnetized; commonly shaped like a horseshoe or a bar.

i.e. compass

electromagnets

a temporary magnet made by wrapping a wire coil carrying a current around an iron core

nonmagnetic

Unaffected by a magnetic field

i.e. wood and glass

diamagnetic

weakly repelled by either magnetic pole. They cannot be artificially magnetized, and they are not attracted to a magnet.

i.e water and plastic.

ferromagnetic

strongly attracted by a magnet and usually can be permanently magnetized by exposure to a magnetic field

i.e. iron, cobalt, and nickel

alnico

a powerful permanent-magnet alloy containing iron, nickel, aluminum, and one or more of the elements cobalt, copper, and titanium.

paramagnetic

somewhere between ferromagnetic and nonmagnetic. They are very slightly attracted to a magnet and are loosely influenced by an external magnetic field

i.e. contrast agents used in MRI

Magnetic susceptibility

the degree to which a material can be magnetized

magnetic poles

two ends of a magnet where the magnetic forces are strongest

North and South (positive and negative electrostatic charges)

SI unit of magnetic field

Tesla (T)

(One tesla (T) = 10,000 gauss (G)

Voltaic pile

A precursor of the modern battery

cell of a battery

Provides the circuit with a source of potential difference. A battery is two or more cells

solenoid

a coil of wire with an electric current in it

electromagnet

a coil that has a soft iron core and that acts as a magnet when an electric current is in the coil

ammeter

A device used to measure current in a circuit

electromagnetic induction

An electric current is induced in an electric circuit if some part of that circuit is in a changing magnetic field.

Faraday's Law

The magnitude of the induced electric current depends on four factors:

1. The strength of the magnetic field

2. The velocity of the magnetic field as it moves past the conductor

3. The angle of the conductor to the magnetic field

4. The number of turns in the conductor

i.e. radio receiption

type of motor used with x-ray tubes

induction motor

induction motor

Powers the rotating anode of an x-ray tube

stators

several fixed electromagnets

transformer

A device that increases or decreases the voltage of alternating current

step-up transformer

a transformer that increases voltage

step-down transformer

a transformer that decreases voltage

closed core transformer

built around a square core of ferromagnetic material

shell type transformer

confines even more of the magnet field lines of the primary winding because the secondary is wrapped around it and there are essentially two closed cores.

This type is more efficient than the closed-core transformer.

Most currently used transformers are shell type.

water is a ____________ material

diamagnetic

The force between magnetic poles is proportional to the ________ of the magnetic pole strengths, divided by the ________ of the distance between them

product; square

type of material that can be made magnetic when placed in an external magnetic field

ferromagnetic

According to Faraday's law, the magnitude of the induced electric current depends on which factor?

Strength of the magnetic field

The autotransformer has one winding and varies with ________ and __________.

voltage; current