Substituting values from the circuit:

Ex + 15 volts + 25 volts - 50 volts = 0

Ex - 10 volts = 0

Ex = 10 volts

FIGURE 28.

DETERMINING UNKNOWN VOLTAGE IN A SERIES CIRCUIT.

The unknown voltage (Ex) is found to be 10 volts.

Using the same idea as above, you can solve a problem in the which the

current is the unknown quantity.

Example: A circuit having a source voltage of 60 volts contains three

resistors of 5 Ohms, 10 Ohms, and 15 Ohms. Find the circuit current.

Solution: Draw and label the circuit (figure 29 on the following page).

Establish a direction of current flow and assign polarities. Next, starting

at any point (point A will be used in this example) write out the loop

equation.