Environmental Engineering Reference
In-Depth Information
R
1
12 ohms
R
T
50 ohms
R
2
12 ohms
R
3
? ohms
FIGURE 10.12
Calculating the value of one resistance in a series circuit in Example 10.13.
R
T
=
R
1
+
R
2
+
R
3
R
T
= 10 + 12 + 25 = 47 W
Equation 10.8 can be transposed to solve for the value of an unknown resistance;
for example, transposition can be used in some circuit applications where the total
resistance is known but the value of a circuit resistor has to be determined.
■
Example 10.13
Problem:
The total resistance of a circuit containing three resistors is 50 ohms (see
Figure 10.12). Two of the circuit resistors are 12 ohms each. Calculate the value of
the third resistor (
R
3
).
Solution:
Given:
R
T
= 50 ohms
R
1
= 12 ohms
R
2
= 12 ohms
R
T
=
R
1
+
R
2
+
R
3
R
3
=
R
T
-
R
1
-
R
2
R
3
= 50 - 12 - 12 = 26 W
Note:
When resistances are connected in series, the total resistance in the circuit
is equal to the sum of the resistances of all the parts of the circuit.
s
eries
C
irCuit
C
urrent
Because there is but one path for current in a series circuit, the same current (
I
) must
flow through each part of the circuit. Thus, to determine the current throughout a
series circuit, only the current through one of the parts must be known. The fact that
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