Electrical Calculations - Basic Mathematics for Water and Wastewater Operators - page 155

Thus,

R
N

10 ohms

2

R

eq ==

= 5 ohms

Note: When two equal value resistors are connected in parallel, they present a
total resistance equivalent to a single resistor of one-half the value of either of the
original resistors.

■ Example 10.22
Problem: Five 50-ohm resistors are connected in parallel. What is the equivalent
circuit resistance?
Solution:

R
N

50 ohms

5

R

eq ==

= 10 ohms

What about parallel circuits containing resistance of unequal value? How is equiv-
alent resistance determined? Example 10.23 demonstrates how this is accomplished.

■ Example 10.23
Problem: Refer to Figure 10.27.
Solution:
Given:
R 1 = 3 ohms
R 2 = 6 ohms
E a = 30 volts

We know that
I 1 = 10 amperes
I 2 = 5 amperes
I T = 15 amperes

and can now determine R eq :

E
I

30

a
T

R === 2 ohms

eq

15

+

10 A

R 1 = 3 ohms R 2 = 10 ohms

-

5 A

15 A

FIGURE 10.27 Illustration for Example 10.23.