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Ohms Law Explained
Series Wiring
Understanding & Calculating Series Circuits
BASIC RULES
A series circuit has certain characteristics and basic rules
summarized here:
1. The same current flows through each part of a series circuit.
2. The total resistance of a series circuit is equal to the sum of
individual resistances.
3. Voltage applied to a series circuit is equal to the sum of the
individual voltage drops.
4. The voltage drop across a resistor in a series circuit is directly
proportional to the size of the resistor.
5. If the circuit is broken at any point, no current will flow.
Let's look at each of these closer to gain an understanding of series
circuits.
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Missing Data Here
COMBINATION SERIES PARALLEL
UNDERSTANDING & CALCULATING COMBINATION CIRCUITS
 INTRODUCTION
A "COMBINATION CIRCUIT" is (as you may have already guessed) a
circuit that is a blend of series paths and parallel paths. See Figure
for a visual explanation. Most circuits are of this variety. Don't be
afraid to tackle these circuits as far as the math goes. You merely
have to break each part of the circuit down into either a series circuit
or parallel circuit. Here's how this is done:
BASICS
 You must first figure out
the resistance of each individual parallel path in the circuit. Let's
take the circuit to the right as an example. There is an 8 Ohm resistor
in series (R1) and two 4 Ohm resistors in parallel, R2||R3 (Note:
The || means that the two resistors are in parallel). To figure out
the total resistance of that section of the circuit we use the
following:
1. Find the resistance of the parallel circuit using the
parallel formula.
1/R = 1/R2 + 1/R3
1/R = 1/4 + 1/4
1/R = .25 + .25
1/R = .5
R2||R3 = 1/.5 = 2 Ohms
 Now that you know the
resistance of the parallel 'subcircuit', you add all the series
resistances. Remember the total resistance of R2||R3 can now be
plugged into the series calculation to figure out the remaining
values using Ohm's Law. See figure to the left.
2: Find the total resistance in the circuit by adding R1 and
R2||R3.
Rt = R1 + (R2||R3)
Rt = 8 Ohms + 2 Ohms
R total = 10 Ohms |
Now that you know the total resistance of the circuit you can figure
out the total amperage using Ohm's Law.
I total = V divide by R total
It = 10V / 10 Ohms
I total = 1 Amp.
From here you can figure out each components voltage drop or
current. |
| The best advice in finding the values for a
combination circuit is to first break each part of the circuit
down into series and parallel sections and follow those formulas.
Once that is complete, combine them for your master
calculations. |
“The amount of current flowing in a circuit made up of pure
resistances is directly proportional to the electromotive forces
impressed on the circuit and inversely proportional to the total
resistance of the circuit.”
Don’t let that quote scare you. It
is not as scholarly as it sounds.
Before going further make sure you
understand:
•
What composes a
circuit.
Basic Electronic Circuits Explained
In this section we will discuss what a circuit is. I won't belabor
the principles of the atom -- let a physics text handle that (boring)
task. Instead let's talk about the facts you will need to know to get
started in electronics.
Circuit
A circuit is a path for electrons to flow through. The path is from a
power sources negative terminal, through the various components and on
to the positive terminal.
Think of it as a circle. The paths may split off here and there but
they always form a line from the negative to positive.
NOTE: Negatively charged electrons in a conductor are attracted to
the positive side of the power source.
Conductor
A conductor is a material (usually a metal such as copper) that allows
electrical current to pass easily through. The current is made up of
electrons. This is opposed to an insulator which prevents the flow of
electricity through it.
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 Simple
Circuit
If we break a circuit down to it's elementary blocks we get:
1) A Power Source -- eg: battery
2) A Path -- eg: a wire
3) A Load -- eg: a lamp
4) A Control -- eg: switch (Optional)
5) An indicator -- eg: Meter (Optional)
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 Series
Circuit
A series circuit is one with all the loads in a row. Like links in
a chain. There is only ONE path for the electricity to flow. If
this circuit was a string of light bulbs, and one blew out, the
remaining bulbs would turn off. 
NOTE: The squiggly lines in the diagram are the symbol for
Resistors. The parallel lines are the symbol for a battery. |
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Parallel
Circuit
A parallel circuit is one that has two or more paths for the
electricity to flow. In other words,
the loads are parallel to each other. If
the loads in this circuit were light bulbs and one blew
out there is still current flowing to the
others as they are still in a direct path from  the
negative
to positive terminals of the battery.
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Combination Circuit
A combination circuit is one that has a "combination" of series and
parallel paths for the electricity to flow. Its properties are a
synthesis of the two. In this example, the parallel section of the
circuit is like a sub-circuit and actually is part of an over-all series
circuit.
•
What
voltage, current and resistance
are.
VOLTAGE, CURRENT & RESISTANCE EXPLAINED
In electronics we are dealing with voltage, current and resistance in
circuits. In the next section we'll learn that by using
Ohm's Law we can determine one value by knowing the other two (For
example: Figure out Current by using Voltage and Resistance values). So
it is important to firmly grasp the basics of Voltage/Current/Resistance
first.
We will describe these electrical terms using an analogy that closely
resembles electronics — HYDRAULICS.
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Voltage
Voltage is the electrical force, or "pressure", that causes current
to flow in a circuit. It is measured in VOLTS (V or E). Take a look
at the diagram. Voltage would be the force that is pushing the
water (electrons) forward.
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Current
Current is the movement of electrical charge - the flow of electrons
through the electronic circuit. Current is measured in AMPERES
(AMPS, A or I). Current would be the flow of water moving through
the tube (wire).
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Resistance
Resistance is anything that causes an opposition to the flow of
electricity in a circuit. It is used to control the amount of
voltage and/or amperage in a circuit. Everything in the circuit
causes a resistance (even wire). It is measured in OHMS (W).
A few people mentioned the diagram for this section was
misleading so I am changing it. Be available soon. |
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In simpler
terms, Ohm’s Law means:
1) A steady increase in voltage,
in a circuit with constant resistance, produces a constant linear
rise in current.
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2) A steady
increase in resistance, in a circuit with constant voltage,
produces a progressively (not a straight-line if graphed) weaker
current.
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Ohm’s Law is a set of formulas used in electronics to calculate an
unknown amount of current, voltage or resistance. It was named after
the German physicist George Simon Ohm. Born 1787. Died 1854.
Knowledge of this Law is often
under-estimated by beginners. I have talked to people that can design
complex circuitry and microprocessor systems that have said, “Ohm’s
Law? What’s that?”.
Unless you know this basic
fundamental building block of electronics, you will never have a strong
foundation to hold up the electronics towers you will be constructing in
the future. Learn Ohm’s Law. Learn it inside and out!
Ohm's Law is a formulation of the
relationship of voltage, current, and resistance, expressed as: 
Where:
V
is the Voltage measured in volts
I
is the Current measured in amperes
R
is the resistance measured in Ohms
Therefore:
Volts = Amps times
Resistance
Ohms Law is used to calculate a
missing value in a circuit.
 In
this simple circuit there is a current of 12 amps (12A) and a resistive
load of 1 Ohm (1W).
Using the first formula from above we determine the Voltage:
V = 12 x 1 : V = 12 Volts (12V)
If we knew the battery was supplying 12
volt of pressure (voltage), and there was a resistive load of 1 Ohm
placed in series, the current would be:
I = 12 / 1 : I = 12 Amps (12A)
If we knew the battery was supplying
12V and the current being generated was 12A, then the Resistance would
be: R = 12/12 : R = 1W
Be sure to check out the
Ohm's Calculator to help you determine circuit values.
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Note:
Remember a battery is not measured in amperage as is commonly
believed with beginners to electronics. The battery supplies the
pressure that creates the flow (current) in a given circuit. The
amperage rating on a battery is "How long the battery will last for
one hour while driving a circuit of that amperage". It is measured
in Amperage-Hours. So a 1000mAh would last for 1 hour in a one amp
circuit. (1000mAh is 1A for one hour) |
An easy way to remember the formulas is
by using this diagram. 
To determine a missing value, cover
it with your finger. The horizontal line in the middle means to divide
the two remaining values. The "X" in the bottom section of the circle
means to multiply the remaining values.
• If you are calculating voltage,
cover it and you have I X R left (V= I times R).
• If you are calculating amperage,
cover it, and you have V divided by R left (I=V/R).
• If you are calculating resistance,
cover it, and you have V divide by I left (R=V/I).
Note:
The letter E is sometimes used instead of V for voltage.
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