Transcript Electrical Theory - s3.amazonaws.com

Electrical Theory
Electrical Theory
• Electrical Theory
– Atoms have a center called a nucleus or
center made of protons (positive
particles) and neutrons (neutral particles)
– Electrons (negative particles) orbit the
nucleus
– And atom may have one of or more
electrons orbiting the atom and at
different distances from the nucleus
– Electrons have the ability to travel, leave
one atom and go to another
Electrical Theory
• Electrical Theory
– In some matter, electrons are bound tightly
together and can leave only with great
difficulty
– In other matter the bond is so relaxed that
electron move easily
– Matter or materials whose electrons can
travel easily are called conductors
– Matter that prohibits the free movement of
electrons to travel are called insulators.
– Metals conduct electricity because they have
a great number of free electrons.
Electrical Theory
• Electrical Theory
– If a negative charged body is
connected to a positive charged body
by a conductor, the electrons will be
attracted to the positive particles.
– Nature prefers everything to be
neutral.
– This flow of electrons is called a
current.
– Equilibrium is a term used to describe
when a balance has been reached.
Electrical Theory
• Electrical Theory
– The difference in concentrations of
these electrons in matter is known as
different potentials.
– Electrical potential is the ability to
provide free electrons.
– In electricity the difference in
potential is measured in volts.
Electrical Theory
• Electrical Theory
– There are two types of currents,
Direct current (dc) and
alternating current (ac).
– Direct current flows in one
direction only.
– Alternating current changes it’s
flow (in reverse) 60 times each
second, known as
60 hertz or
60 cycles.
– A cycle is one complete electrical
wave or vibration.
Electrical Theory
• Electrical Theory
– To maintain a flow of electron it is
necessary to have a source which is
always at a greater electrical potential.
– Meaning to always have an excess of
free electrons.
– That energy can be produced chemically
(battery) or mechanically (generator).
Electrical Theory
• Electrical Theory
– Battery (voltaic cell)
• Copper and zinc rods
• Acid solution
• Acid strips electrons from the copper
rod
• Electrons travel to the zinc rod
• Resulting in the copper rod having less
electrons and becoming the positive
pole (anode).
• The zinc rod having an excess of
electrons and becoming the negative
pole (cathode).
Electrical Theory
• Electrical Theory
– Battery (voltaic cell)
• A group of cells is called a battery
• Circuit is produced when there is a
conductor and a load placed on the positive
and negative ends of the battery.
– Dry cell or wet cell
• Dry cell use a chemical paste (acid paste)
– Used in remotes, walkmans, & cameras
• Wet cell uses a liquid chemical (acid)
– Used in your car
Electrical Theory
• Electrical Theory
– No electron flow without a
pathway
– The pathway is known as a circuit.
– A simple circuit needs:
•
•
•
•
A power source.
Conductors.
A load or loads.
A device for controlling current.
Electrical Theory
Electrical Theory
• What happened when a pathway was place
from the battery to the load and back to the
battery?
• Remove the conductor from the positive post.
What happens?
• Open and Closed circuit.
• In Theory explain what is happening inside the
battery and what happens when the circuit is
closed.
Electrical Theory
Electrical Theory
• What purpose does the switch serve?
• Relate an electrical switch to a water
supply system.
• I this a series or a parallel circuit?
• Where is the load?
• What happen if there is no load? The
connection is made from pole to pole
with no energy being used?
Electrical Theory
Electrical Theory
• What is different?
• Why?
• In a series circuit the resistance on one
device affects the rest of the loads on
the circuit.
• How can this affect can this have on
equipment or appliances?
• Wire the three loads using a parallel
circuit.
Electrical Theory
Electrical Theory
• What is different?
• Why?
• Which type of circuits do think is
generally used in homes?
• Place a device to open and close each
lamp/load on the circuit.
Electrical Theory
Electrical Theory
• How does this circuit differ from the
from the previous series circuit?
• What are the advantages of a parallel
circuit?
Electrical Theory
Ohm’s Law
Current in a circuit is directly
proportional to the voltage
applied to the circuit and is
inversely proportional to the
resistance of the circuit
Electrical Theory
The rate of the flow of the current is equal to
electromotive force divided by resistance
• I = Intensity of Current = Amperes
• E = Electromotive Force + Volts
• R = Resistance = Ohms
• P = Power =Watts
• The Three Basic Ohm’s Law Formulas are:
I= E
R
R=
E
I
E=IxR
Electrical Theory
E
I
R
Electrical Theory
P
Power
(Watts) W
Resistance
(OHMS) Ω
R
I
Current
(Amps) A
Voltage
(Volts) V
E
Electrical Theory
Electrical Theory
Ohm’s Law
An electric appliance is rated at 1200 Watts,
and connects to a 120 Volt outlet. How much
will it draw? (amps)
Amperes =
Watts
Volts
I=
P
E
I=
1200
120
= 10A
What is the Resistance of the same appliance?
Ohm’s =
Volts
Amperes
R=
E
I
R=
120
10
= 12 Ω
Electrical Theory
Ohm’s Law
Series Circuits
In the example, we know the following values:
I = amps = 10
R = ohms = 12Ω
E = volts = 120
P = watts = 1200
Electrical Theory
Ohm’s Law
Series Circuits
• What is given?
– Ohms
• 1Ω + 2Ω + 3Ω = 6Ω
– Volts
• Given 6volts
– What value do we
need?
– Amperage (I)
• 6volts ÷ 6Ω = 1 Amp
Electrical Theory
Ohm’s Law
Series Circuits
E = 6 volts
• Calculate the watts
from the same circuit.
• What method can be
used?
–
–
–
–
P = E x I, I2R, E2 ÷R
E x I = P, 6 x 1 = 6 watts
I2R, 12 x 6 = 6 watts
E2 ÷R, 62 ÷ 6 =6 watts
R = 6 ohms
I = 1 amp
P = ?? 6 watts
Electrical Theory