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TM 9-254
7-2.
Direct Current - Continued
(2)
The general formula for any number of unequal value resistors in parallel is:
Figure 7-3. Parallel Circuit
(3)
There are several special cases regarding parallel resistances.
(a)
The first case relates to a circuit with only two unequal value resistors in parallel. In this case the
equivalent resistance can be found by dividing the product of the two resistors by their sum. This is
stated mathematically as follows:
RT
= R1
R2
R1 + R2
(b)
The second special case involves any number of equal value resistors in parallel. The equivalent
resistance is found by dividing the resistance of one resistor by the number of resistors in parallel
or:
RT =
R
n
Where:
RT
is the equivalent resistance.
R is the resistance value of each resistor.
n is the number of resistors in parallel.
7-3
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