BASIC DC CIRCUIT CALCULATIONS
Basic DC Theory
Example 2:
Now add a fourth resistance of 4W in parallel to the circuit in Figure 27. What
is the new total resistance of the circuit?
Solution:
1
RT
1
R1
1
R2
1
R3
1
R4
1
RT
1
4
1
8
1
16
1
4
1
RT
4
16
2
16
1
16
4
16
11
16
RT
16
11
1.45W
Simplified Formulas
Total resistance of equal resistors in a parallel circuit is equal to the resistance of one resistor
divided by the number of resistors.
RT
R
N
where
RT
=
total resistance
R
=
resistance of one resistor
N
=
number of resistors
Example:
Five lamps, each with a resistance of 40W, are connected in parallel. Find total
resistance.
R
R1
R2
R3
R4
R5
40W
N
5
RT
R
N
40
5
8W
ES-02
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