BASIC ELECTRONICS - OD1633 - LESSON 1/TASK 2
NOTE
The subscript n denotes any number of
additional
resistance that might be in the equation.
Example: In figure 20 a series circuit consisting of three resistors--one of
10 Ohms, one of 15 Ohms, and one of 30 Ohms--are shown. A voltage source
provides 110 volts. What is the total resistance?
Given:
R1 = 10 Ohms
R2 = 15 Ohms
R3 = 30 Ohms
Solution:
RT = R1 + R2 + R3
RT = 10 Ohms + 15 Ohms + 30 Ohms
RT = 55 Ohms
In some circuit applications, the total resistance is known and the value of
one of the circuit resistors has to be determined. The equation RT = R1 +
R2 + R3 can be transposed to solve for the value of the unknown resistance.
Example: In figure 21 (on the following page) the total resistance of a
circuit containing three resistors is 40 Ohms. Two of the circuit resistors
are 10 Ohms each. Calculate the value of the third resistor (R3).
Given:
RT = 40 Ohms
R1 = 10 Ohms
R2 = 10 Ohms
Solution:
RT - R1 - R2 = R3
Subtract R1 + R2 from both sides of the equation
R3 = RT - R1 - R2
R3 = 40 Ohms - 10 Ohms - 10 Ohms
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