Download What is electricity?

What is electricity?
• Electricity is the flow (movement) of
electrons!
Conductor vs. Insulator
• Conductors are materials that allow an
electric current to pass.
– Metals
• Insulators are materials that do not allow an
electric current to pass
– Nonmetals, plastic, glass, wood, rubber
Two Main Types of Electricity
• Static Electricity – Electric charges (electrons)
that buildup and collect on an object
Static Electricity
• When you rub two objects together…a balloon
and your hair…electrons are transferred from
one object to the other
Van de Graaff Generator
AC vs DC Current
• Direct Current – The electrons flow steadily in
a single direction
• Alternating Current - The electrons keep
switching directions, sometimes going
“forwards” and then going “backwards”
• Any movement of electrons is a current!
•
AC vs DC Current Video
AC/DC
• The band AC/DC chose the name to symbolize
the bands “raw energy” when performing
How is an Electric Current Generated?
• Scientists found that electrical and magnetic
fields are related
• A magnetic field near a wire causes electrons
to flow in a single direction along the wire
– This is because the electrons are repelled and
attracted by the north and south poles
–
Electric Current Generation Video
DC Electric Motor
• An electric motor is simply a generator with a
power source attached
– This causes the wire to spin because of the
opposing charges provided by the battery
Making Our Own Simple DC Motor
The AC vs DC War
• In the late 1800’s Thomas
Edison promoted the use
of DC current as a
standard
• During the first few years
of electrical distribution
DC current was the
standard for the US
Westinghouse
Edison
• George Westinghouse
was a proponent of
using AC current
• Edison did not believe
AC current would work
efficiently (he also held
all the patents for DC
current use)
The AC vs DC War
• Advantages of DC
– Was easy to make DC run at a voltage that could
be widely used (100 volts)
– DC motors were common (AC motors were not)
– Could be used with batteries easily (Chemical
batteries provide DC power)
• Disadvantages of DC
– Generating plants (or substations) were required
within one mile of the load (homes)
• This is due to the high resistance nature of running low
voltage
The AC vs DC War
• Advantages of AC
– Could be transmitted at very high voltages
(100,000 or more)
• This allowed it to be transmitted much further without
as many substations (100’s of miles)
• Disadvantages of AC
– AC motors were rare, and expensive
– To charge a battery a power inverter is required
(converts AC  DC)
Michael Faraday
• In 1831 Faraday discovered electromagnetic
induction
– He discovered that a changing magnetic field is
necessary to induce a current in a nearby wire
(circuit)
• This is the basis of an electrical generator
Voltage, Current, Resistance
• What’s the difference?!
Abbreviation
Measured in
Voltage
V (or E)
Volts (v)
Current
I
Amperes (amps)
Resistance
r
Ohms (Ω)
Voltage
• Voltage is defined as the “potential difference”
from one point on a circuit to another
– Think of voltage as the water pressure in a hose
• A voltage can be measured even when no
electrons are moving between the points as it is a
measure of potential energy that will not be
released until the electrons begin to flow.
– Even if water valve is closed, there is still pressure
(voltage)
Current
• Current is the rate of flow of electrons
– This is like the amount of water flowing through a
pipe
• One amp = 1 coulomb per second
– One coulomb = = 6.242 × 1018 electrons
– 6,242,000,000,000,000,000 electrons per sec.
Resistance
• Resistance is the opposition to the passage of
a steady electric current
Two things can affect resistance: thickness of the
wire, and the material the wire is made out of
Ohms Law!!!
I = V/R
To make a current flow through a resistance
there must be a voltage across that resistance
What is the current that flows through a
circuit that is supplied with 120 volts and has
a resistance of 52 ohms?
What are electric circuits?
Circuits typically contain a voltage source, a wire conductor,
and one or more devices which use the electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway for the
current to flow. If the circuit breaks, all devices using the
circuit will fail.
What is a parallel circuit?
A parallel circuit has multiple pathways for the current to
flow. If the circuit is broken the current may pass through
other pathways and other devices will continue to work.
Resistance in Series vs. Parallel Circuits
• Resistance is higher in series circuits because
the electrons only have one path to follow
• Rtotal = R1 + R2 + Rn
• Resistance is lower in parallel circuits because
the electrons can flow along many paths
Power Source
• Provides a specified voltage to provide current
to your circuit
Resistors
• Decrease current flow in a circuit
• Dissipate power (usually in the form of heat)
Capacitors
• Capacitors store energy
• This allows many things
– Can be used to supply power even when power if
off (for a short time)
– Can “buffer” power supply when high current
draw
LED’s
• Light Emitting Diodes
– Special type of diode that
emits light
– Very low power
consumption
– Come in all sorts of colors
Transistors
• Transistors allow a small
current (mA’s) to trigger a
larger current flow
• Small current goes into the
base and allows larger current
to flow through the collector
and emitter
Sort of like
a switch
Integrated Chips (IC’s)
• Chips contain tens,
hundreds, or even
thousands of components
inside them
• For example a 555 Timer
contains:
– 20 transistors
– 2 diodes
– 16 resistors