Intro to Electronic

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Transcript Intro to Electronic

Intro to Electricity
What is electricity?
How is it created?
How is it transmitted?
Electricity
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Electricity is a form of energy
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Generally defined as the flow of electric charge
from one place to another
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This is not entirely accurate, but the metaphor works
Two sub-atomic particles
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Protons
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Positive charge. Large relative mass
Electrons
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Negative charge. Very little relative mass
Electricity
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Electric power is created by detaching electrons
from an atom
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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
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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
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Voltage will change with
time
In most instances, it
happens very fast
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50 cycles per second (Hz)
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Europe and most of Asia
60 cycles per second (Hz)
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United States, some of Asia
and some South America
Alternating current
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James Clerk Maxwell
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Discovered that electricity and magnetism are two forms of the same physical phenomenon.
Maxwell’s laws
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“A changing magnetic field will produce an electric field”
“A changing electric field will produce a magnetic field”
How a generator works
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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
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Causes three phase electricity. The number of times per sec that the coil revolves will determine the frequency of the
electric current
Induced current
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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
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Often the product of a chemical reaction
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Batteries
Can be generated using an alternator
Can be converted from AC current
Voltage stays constant over time.
Ohms Law
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Voltage, current and resistance
are all related
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Voltage – Also called
Electromotive Force (EMF)
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The potential charge between
two points
It is a relative measurement
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We usually measure voltage
with respect to “ground” or
“earth”
Requires a complete path
back to ground in order to
“flow”
Current
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The “flow” of electrical charge
carriers
Current Flow
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Water analogy
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Wire = hose
Voltage = water pressure
Current = flow of water
Resistance = resistance to water flow
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Kink in the hose
A larger hose connected to a smaller hose
Ohms Law
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V=IR
P=VI
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V= voltage (volts)
I = current (amps)
R = resistance (ohms)
P = power (watts)
VIRP
Ohms Law
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These two formulas allow us to relate
voltage, current resistance and power to each
other.
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If you know any 2, you can now the other 2.
Strictly speaking this is only for DC circuits
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For AC circuits, resistance is replaced with
impedance
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Takes into account capacitors and inductors
Circuits
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Series
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Electricity flows through
each component
RT=R1+R2+R3…
Circuits
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Parallel
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The current breaks up,
with some flowing along
each parallel branch and
re-combining when the
branches meet again.
1
1
1
1
 
 ....
RT R1 R2 R3