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- Assuming that you are already
familiar with electricity, let's take a look into circuits.
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- To clearly define a circuit,
it is easy to understand it as a repetition of work. Electric
current flows from the - side to the + side all
the time, and it is called a circuit.
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- There are different types of
circuits, but the easiest of them all is a series circuit.
A series circuit only has one path for the electric current to
flow. Here is an example of a series circuit:
- As you can see, this example
circuit only has one path for electron flow.
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- To be able to distinguish between
current (I), resistance (R) and voltage (E),
you have to understand Ohm's Law. Here is the formulae:
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I = E / R |
E = IR |
R = E / I |
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- With any of the two variables
known, you can always find the third value. To make it easier
to remembers these formulas, you can engrave this little hint
into your brain:
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If you remember this circle in
your head, then you wont have any problems with Ohm's Law.
If you know I and R, E = IR.
If you know E and I, R = E / I, and so forth. That's all there
is to it. |
- There are a few abbreviations
for voltage, resistance and current, but I tend to stick to the
common sense ones:
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E
= Electromotive Force (EMF) (Voltage) |
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R
= Resistance |
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I
= Current (Ok...not that obvious) (When on a schematic diagram,
I stands for lamp, and I is used to represent the word incandescent) |
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- The best way to get a grip on
these formulas, is to actually use them in a real life situation.
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- Take a look here; these are
some problems to work with. Practice them:
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I = E / R |
E = IR |
R = E / I |
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Looking at the formulas above,
practice these problems, but do not worry about the meaning of
voltage, resistance or current. Get used to doing the problems.
It's like an algebra review.
Voltage = 9v |
Resistance = 5W | Current = x
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Answer:
x (I) = E / R = 9v / 5W = 1.8a |
Current = 3.5a |
Resistance = 9W |
Voltage = x
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Answer:
x (E) = IR = 3.5(9W) = 31.5v |
Current = 2.7a | Voltage
= 15v | Resistance = x
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Answer:
x (R) = E / I = 15 / 2.7
= 5.56W |
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- Now let's take a look at the
three elements in more depth.
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- Voltage ( E or V )
- in simple terms, it is the electrical pressure, or Electromotive
Force (EMF)
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- Current ( I ) - current
is the flow of electrons. The current is the actual worker in
a circuit
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- Resistance ( R ) - resistance
is anything that opposes the flow of current
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- The schematic symbol for a resistor
would look similar to this:
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- Voltage is the pressure that
pushes the electrons. Some common ways to produce voltage is
by friction and magnetic. This pressure is measured in volts
( v ). A volt is measure of potential difference.
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- Current is the flow of electrons.
Current ( I ) is measured in amperes. One amp is ..::
6.28 x 10^18 ::.. electrons in one place of the
circuit per second. This rate is measured in coulombs.
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- Resistance ( R ) is measured
in Ohms ( W ). One Ohms of resistance is equal to
1v divided by 1amp. There are components in eletronics called
resistors. How much resistance there is, is determined
by the color code (Not really, but it tells us how much there
is, the actual resistance is inside, done by chemical work).
I have a resistor color code chart
here on the page.
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- On the circuits provided by
myself, I will almost always label voltage with E, but
on other circuits, you will probably see a V for voltage.
Both mean the same thing.
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- You've already seen a schematic
that I've provided at the top of this page. In this section I
will stick with series circuits, because they are much
simpler, but very important to learn.
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- You've worked with Ohm's Law,
so now, let's take a look at a couple of circuits and find out
values. For the next couple of circuits, look at the picture
and write down the work on a separate sheet of paper. Here goes...
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R = 20W | E = 100v
| I = x
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Answer:
x (I) = E / R = 100 /
20 = 5a |
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E = 15v | I = 2a | R = xW
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Answer:
x (R) = E / I = 15 / 2
= 7.5W |
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R = 30W | I = 51
| E = x
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Answer:
x (E) = IR = 30 x 5 =
150v |
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- Hopefully, you didnt get anything
wrong, because the equations are simple so far. Take this quiz,
to test your overall knowledge of this page.
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1 |
What is electricity? |
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2 |
From which direction does the current
flow? |
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3 |
What elements of the Ohm's Law are
there? |
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4 |
What does the symbol for a resistor
look like? |
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5 |
What does EMF stand for? |
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6 |
Rate at which amps are measured,
is called what? |
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7 |
What is the resistor value of this
color code? [ Red | Yellow | Green ] |
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8 |
State one way to generate electric
current? |
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9 |
E
= 10v / I = 15a / R = xW |
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10 |
I
= 1a / R = 5W / E = x |
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Got everything correct? Check your
answers here. |
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