Electrical Calculations - Basic Mathematics for Water and Wastewater Operators - page 150

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E b v R 1 v R 2 v

10 V 10 V 10 V

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FIGURE 10.19 Voltage comparison in a parallel circuit.

We can verify Equation 10.11 by taking voltage measurements across the resistors of
a parallel circuit, as illustrated in Figure 10.19. Notice that each voltmeter indicates
the same amount of voltage; that is, the voltage across each resistor is the same as
the applied voltage.
Note: In a parallel circuit, the voltage remains the same throughout the circuit.

■ Example 10.17
Problem: Assume that the current through a resistor of a parallel circuit is known to
be 4 milliamperes (mA) and the value of the resistor is 40,000 ohms. Determine the
potential (voltage) across the resistor. The circuit is shown in Figure 10.20.

Solution:
Given:
R 2 = 40,000 ohms
I R 2 = 4 mA

Find E R 2 and E b . Select the appropriate equation:

E = I × R

Substitute known values:

E R 2 = I R 2 × R 2 = 4 mA × 40,000 ohms

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R 1 R 2

40 kΩ

R 3

E b

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FIGURE 10.20 Illustration for Example 10.17.