Intro to Electricity
What is electricity?
How is it created?
How is it transmitted?
Electricity
Electricity is a form of energy Generally defined as the flow of electric charge
from one place to another This is not entirely accurate, but the metaphor works
Two sub-atomic particles Protons
Positive charge. Large relative mass Electrons
Negative charge. Very little relative mass
Electricity
Electric power is created by detaching electrons from an atom This leaves behind a net positive charge This positive charge pulls electrons from neighboring
atoms and a “flow” begins Not all atoms easily allow their electrons to break
free Good conductors – easily freed electrons
Copper, aluminum, gold, platinum Insulators – electrons are VERY hard to break free
Most plastics, silicone rubber, porcelain, glass
Alternating current
Voltage will change with time
In most instances, it happens very fast 50 cycles per second (Hz)
Europe and most of Asia
60 cycles per second (Hz) United States, some of Asia
and some South America
Alternating current James Clerk Maxwell
Discovered that electricity and magnetism are two forms of the same physical phenomenon. Maxwell’s laws
“A changing magnetic field will produce an electric field” “A changing electric field will produce a magnetic field”
How a generator works 3 massive coils of wire which are caused to spin around a permanent magnet. Coils are moving through a magnetic field and this causes electrons to begin moving While moving from north to south, electrons flow one way. From south to north they move the other way
Causes three phase electricity. The number of times per sec that the coil revolves will determine the frequency of the electric current
Induced current As the voltage rises and falls in an AC circuit, there will be a varying magnetic field produced around
the conductor. This magnetic field will in turn produce an electric current in any conductors which are nearby
Lighting cable, motor cable, sound power feeds, building air conditioning power… Induces noise in sound lines
Direct current
Often the product of a chemical reaction Batteries
Can be generated using an alternator Can be converted from AC current Voltage stays constant over time.
Ohms Law Voltage, current and
resistance are all related Voltage – Also called
Electromotive Force (EMF) The potential charge between
two points It is a relative measurement
We usually measure voltage with respect to “ground” or “earth”
Requires a complete path back to ground in order to “flow”
Current The “flow” of electrical charge
carriers
Current Flow
Water analogy Wire = hose Voltage = water pressure Current = flow of water Resistance = resistance to water flow
Kink in the hose A larger hose connected to a smaller hose
Ohms Law
V=IR P=VI
V= voltage (volts) I = current (amps) R = resistance (ohms) P = power (watts)
VIRP
Ohms Law
These two formulas allow us to relate voltage, current resistance and power to each other. If you know any 2, you can now the other 2.
Strictly speaking this is only for DC circuits For AC circuits, resistance is replaced with
impedance Takes into account capacitors and inductors
Circuits
Series Electricity flows through
each component RT=R1+R2+R3…
Circuits
Parallel The current breaks up,
with some flowing along each parallel branch and re-combining when the branches meet again.
1 2 3
1 1 1 1....
TR R R R
