Transcript Basic Electricity - UHCL-TRC

Basic Electricity
DC and AC
What is Electricity?

Electricity is a general term used for the
presence and flow of electric charge .

In more scientific terms, it is the flow of
electrons from one place to another.
Types of Electricity
Static – Metal door handles on cold dry
mornings (OUCH!)
 Stored – Batteries, etc.
 Generated- Provides our homes and
schools with power.
 All deal with the flow of electrons from
one point to another.

Electrons?

As we know, an atom is made up of subparticles, those being:
 ELECTRONS
(negatively charged)
 PROTONS (positively charged)
 NEUTRONS (neutral, no charge)
ELECTRON (-)
PROTONS (+) &
NEUTRONS (0)
Electron Flow
To illustrate the most basic form of
electron flow, we use something called a
circuit.
 The circuit is made up of a power source,
conductors (wires) to provide a path for
the electrons to flow, and a useful device
such as a light bulb (also called a LOAD)

The Basic Circuit
NEGATIVE ( - )
POSITIVE (+)
Electrons flow NEGATIVE to POSITIVE
The Circuit Shown Here is a
DC (Direct Current) Circuit

In a DC Circuit, there is only ONE direction for
current flow.
Note the switch opens, current stops flowing.
DC Circuits

Direct Current is provided to us
mostly by batteries, used in :
–
–
–
–
–
Flashlights
iPods
Laptop Computers
Automobiles
Solar Cells
DC Series Circuits


Loading batteries in a flashlight is a good
example.
Batteries are placed end to end, positive to
negative.
_
+
1.5 volts
_
_ +
+
1.5 volts
1.5 volts
Batteries in Series




When batteries are installed this way, they
are said to be AIDING one another.
If three 1.5 volts batteries were installed in a
flashlight, what would the total voltage be ?
3 X 1.5 =
4.5 volts
Parallel




If batteries are connected in parallel,
something completely different happens.
A good example of this is connecting jumper
cables between car batteries.
A car battery is 12 volts.
If the cables were hooked up in SERIES,
12 + 12 = 24 volts, and the starter would be
TOAST!
Parallel Circuits




Instead, Positive is connected to Positive.
Negative is then connected to Negative.
The voltage remains at 12 volts – it does not increase.
What DOES increase is the amount of electrical current
to turn over a weak starter.
Series vs. Parallel



Each have their use
SERIES increases voltage (add voltages)
PARALLEL increases current.
WHAT IF A BULB GOES OUT IN EITHER
SITUATION? WHAT WILL HAPPEN TO
THE OTHER BULBS?
SERIES- 3 bulbs drop 4
volts each to divide the load.
3 times 4 = 12.
PARALLEL – 12 volts is present
EVERYWHERE in the circuit
AC Current
A more complicated type of
current is AC, or Alternating
Current.
 Like DC, it involves the
movement of electrons.
 Unlike DC, AC electrons move in
one direction, then they reverse.
 This means that current flows
one way, then the other.

AC
AC power is provided to us by our electric
company.
 Without it, life would be rather dull (and
DARK)
 AC powers just about everything in our
homes that use electricity.
 When you plug a power cord into a wall
outlet, you are using AC.

AC – Alternating Current
AC is created by a device called a
generator (or ALTERNATOR)
As a result of magnetic field being cut by a
conductor, AC is produced.
AC in its simplest form is represented by
something called a SINE WAVE…….
The AC Sine Wave
How The Sine Wave Is Produced
The SINE WAVE
90 dg
180
180dg
360 dg
0 dg
270 dg
This drawing represents how a sine wave looks when viewed
through an oscilloscope
Producing AC Sine Waves
Electrical Waveforms
Alternating current or voltage
Pulsating direct current or voltage
Fluctuating direct current or voltage
Basic Generator
Generating A Sine Wave
S
0
degrees
N
Motion is parallel to the flux. No voltage is induced.
Generating A Sine Wave
S
x
N
Motion is 45 to flux. Induced voltage is 0.707 of maximum.
Generating A Sine Wave
S
90 degrees
x
N
Motion is perpendicular to flux. Induced voltage is maximum.
Generating A Sine Wave
S
x
N
Motion is 45 to flux. Induced voltage is 0.707 of maximum.
Generating A Sine Wave
S
180
degrees
N
Motion is parallel to flux. No voltage is induced.
Generating A Sine Wave
S
x
N
Notice current in the conductor has reversed.
Motion is 45 to flux. Induced voltage is 0.707 of maximum.
Generating A Sine Wave
S
270
degrees
x
N
Motion is perpendicular to flux. Induced voltage is maximum.
Generating A Sine Wave
S
x
N
Motion is 45 to flux. Induced voltage is 0.707 of maximum.
Generating A Sine Wave
S
360
degrees
N
Motion is parallel to flux. No voltage is induced.
Ready to produce another cycle.
WHY AC ?
BECAUSE OF ITS VERSATILITY
AC IS EASIER TO GENERATE
AC IS EASIER TO TRANSMIT
AC IS EASIER TO STEP-UP OR
DOWN
AC IS MORE ECONOMICAL
Producing AC
AC GENERATING STATIONS USE A
VARIETY OF METHODS TO PRODUCE
ELECTRICITY
 HYDROELECTRIC
 STEAM
 COAL
 NUCLEAR…..ARE MEANS OF OPERATING
THE TURBINES THAT PRODUCE THE
ELECTRICITY

Generating AC
THE VOLTAGE THAT LEAVES THE
GENERATING STATION IS VERY HIGH
 APPROX. 275,000 VOLTS OR MORE
 THE ELECTRICITY MUST BE STEPPED
DOWN BEFORE POWERING OUR HOMES
 HOUSEHOLD CURRENT IS 120/240 VOLTS
AT 60 HERTZ
 TRANSFORMERS ARE USED TO STEP
DOWN VOLTAGE FROM HIGH TO LOW

Transformers
Other AC Uses
AC IS USED IN TELECOMMUNICATIONS
 AC SIGNALS ALLOW INTELLIGENCE TO BE
XMITTED OVER LONG DISTANCES
 A XMITTING ANTENNA CONVERTS AC
SIGNALS INTO ELECTROMAGNETIC
WAVES
 THE SIGNAL THAT REACHES RADIOS AND
TV’S IS AC

More About AC
AC is not only measured in VOLTS, but also in a
unit called the HERTZ.
 The HERTZ is a unit of measuring time, called
FREQUENCY.
 The electricity in our houses makes 60 complete
cycles per second, therefore its frequency is 60
HERTZ.

More Uses for AC

Sometimes AC power is all that is
available, but you have a device such as a
music player that operates on batteries.

What do you do ??????????????
Converting AC to DC
By using a Power Supply, the AC wave is cut in
half and filtered so that it becomes smooth DC.
 AC adapters perform this task.

120 VAC
12
VAC
12 V DC
SAFETY FIRST !

When working around electricity, one must
observe some basic precautions:
 Never
work with electricity when wet.
 Be careful that metal objects or liquids don’t
come in contact with electricity.
 NEVER pour water on an electrical fire!!
 Try to use only one hand if at all possible.
 Electricity is something we can’t see (but can
sure feel if we goof up!)
What did we learn?

What is the difference between AC and DC?

What is the difference between a SERIES and a
PARALLEL circuit ?

What is a common household voltage?

What is the basic AC wave called?
The End