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Resistors in parallel
are connected across one
another.
They all have the same
voltage across them.
To find the equivalent
resistance (the total
resistance offered to
the flow of current) we
invert the values and
add them. Then we invert
the result.
For example take 2 ohms
and 4 ohms in parallel.
Inverted 1/2 +1/4 = 3/4
Invert this 4/3 = 1.33
ohms
A quick check on your
answer is that it should
be smaller in value than
the value of the
smallest resistor.
If these resistors were
connected across a 10
volt supply Ohms Law
says about 7.5 amps
would flow.
The formula can be
written as 1/Rtotal =
1/R1 + 1/R2 + 1/R3 etc
etc.
If only two resistors
are involved then use
(R1 x R2) divided by (R1
+ R2)
For the 2 ohms and 4
ohms.
R1 x R2 = 8.
R1 + R2 = 6.
8/6 = 1.33 ohms
If you have several
resistors of the same
value in parallel then
the equivalent
resistance is the
resistor value divided
by the number of
resistors.
For example, four 100
ohm resistors in
parallel will provide a
resistance of 25 ohms
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