BASICS OF ELECTRICITY Vocabulary Understanding of Layer 1 & Layer 2 Networking Professionals need a basic understanding.

BASICS OF ELECTRICITY

• Vocabulary

• Understanding of Layer 1 & Layer 2

• Networking Professionals need a basic understanding

ATOMIC STRUCTURE

• All matter is composed of atoms– Listed on Periodic Table

ATOMIC PARTS

– Nucleus• Center of the atom

– Protons and neutrons

– Protons• Positively charged particles

– Neutrons• Neutral change

– Electrons• Negative charge

• Orbit the nucleus

HELIUM EXAMPLE Bohr’s Model

Atomic Number = 2Atomic Weight = 4Atomic Weight - Atomic Number =

# of Neutrons

2 Neutrons2 Protons2 Electrons

ATOMIC SCALE

• Protons & Neutrons the size of a soccer ball

• Electrons the size of cherries

• Nucleus in the middle of a soccer field

• Electrons orbiting at the outermost seats of the stadium

COULOMB’S ELECTRIC FORCE

LAW• Opposite charges attract

• Like charges repel

• The closer the charges come, the greater the force of attraction or repulsion

WHY DON’T THE ELECTRONS FLY IN

TOWARD THE PROTONS?

• The electrons have just enough orbiting velocity to prevent being pulled into the nucleus

• Weak force

WHY DON’T THE PROTONS FLY AWAY FROM EACH OTHER?

• Nuclear force is associated with Neutrons

• Incredibly strong force which holds the Protons together

ELECTRICITY

• Nuclear forces bind the nucleus together strongly

• Weak force holds the electrons in orbit– If the electrons are pulled free

from the atom, they can be made to flow

• Electricity is the “free flow of electrons”

STATIC ELECTRICITY

• Loosened electrons, negatively charged, that stay in one place

• Prone to “jump” to a conductor– Leads to Electrostatic Discharge

(ESD)• Usually harmless to people

• Can randomly damage computer chips and/or data

– Proper handling techniques essential

» ESD straps, mats

» handle components by non-conducting edges

MATERIALS

• Atoms & Molecules (groups of atoms)

• Classified by the ease with which free electrons (electricity) flow through them– Insulators– Conductors– Semiconductors

INSULATORS

• Electrons flow with great difficulty or not at all

• Plastic, glass, air, dry wood, paper, rubber, helium gas

• Very stable chemical structures– Orbiting electrons tightly bound

within the atom

CONDUCTORS

• Electrons flow very easily

• Best conductors are metals: copper, silver, gold

• Also good conductors: solder (lead and tin) and ionized water– An ion is an atom with more or

less electrons that a neutral atom– An ion is, therefore, a charged

particle– Human body is 70% ionized

water, so it conducts well

• Outermost electrons of the atom are loosely bound and readily freed

SEMICONDUCTORS

• Flow of electrons can be precisely controlled

• Most important: silicon

• Also carbon, germanium, gallium arsenide

ELECTRICAL MEASUREMENT

TERMS• Voltage

• Current– Alternating Current– Direct Current

• Resistance

• Impedance

• Ground

VOLTAGE

• Electrical pressure due to the separation of electrical charge (+ and -)– e.g. batteries

• Can also be created by friction (static electricity), by magnetism (generator), or by light (solar cell)

• Represented by V

• Unit of measurement is volt

• Definition: The amount of work, per unit charge, needed to separate the charges

CURRENT

• Flow of charged particles– usually electrons

• Voltage causes currents– When voltage (electrical pressure)

is applied, and there is a path for the current, electrons move from the negative terminal (repelled) to the positive terminal (attracted)

• Represented by I

• Unit of measurement ampere (amp)

• Definition: Number of charges per second that pass by a point along a path

ALTERNATING CURRENT

• Current and voltages vary with time by changing polarity (direction)– AC flows from positive to

negative– Polarity of terminal is reversed– AC flows in other direction– Process repeats continuously

• Carried on utility power lines

DIRECT CURRENT

• Always flows in the same direction

• DC voltages always have the same polarity– Terminal polarities do not change

• Battery power, power for microchips on the motherboard

RESISTANCE• Property of a material that

opposes electrical flow• Materials with high resistance are

insulators

• Materials with low resistance are conductors

• Amount of resistance depends on the chemical composition of the material

• Represented by R

• Unit of measurement is ohm (W or Ω)

• Generally used to refer to DC current

IMPEDANCE

• Total opposition to current flow

• Analogous to resistance– General term, but applied to AC

and pulsed circuits

• Represented by Z

• Unit of measurement is ohm (W or Ω)

GROUND• Term is used in many ways

• Can mean the place on the earth that touches a building– gives electrons an extra

conducting path to flow to the earth

– protects your body from shock

• Can mean the 0 volts reference level for electrical measurements– Voltage is created by the

separation of charges• measurement must be made between

two points

VOLTAGE, CURRENT, AND RESISTANCE

WORKING TOGETHER

• Electrons flow in closed loops called circuits– Voltage causes current to flow– Loop must be made of a conducting

material– Resistance and Impedance oppose the

flow of current

• Using Voltage and Resistance/Impedance allows people to control the flow of a current

• Multimeters measure voltage, current, resistance/impedance

GRAPHING AC & DC VOLTAGE

• Oscilloscopes– Device used to study electrical

signals:

•X-axis represents time

•Y-axis represents voltage

A SIMPLE SERIES CIRCUIT

•Chemical processes in the battery cause separation of charges which provides a voltage to “push” the electrons along the conducting wire

•Switch allows the circuit to be open (current flows) or closed (no current flow)

•Bulb provides resistance

•Electrons release energy in the form of light

GROUNDING EQUIPMENT

• Outlets have two power connectors plus a safety ground connector– Safety ground wire in electrical

equipment (including computing equipment) is connected to exposed metal

– Prevents metal parts from being energized with hazardous voltage

• Electrical current follows path of least resistance and drains off to earth

• Protects body by diverting current