P 3.2-12 Determine the voltage and current of each of the circuit elements in the circuit shown in Figure P 3.2-12.

Figure P 3.2-12

We have six circuit elements, 15 V Source, 0.75 A Source, and 0.25 A Source, 60 Ω Resistor, 10 Ω Resistor, and 20 Ω Resistor. Now the Voltage for the 15 V source is obviously 15 V, and the current for the 0.75 A source is 0.75 A and the current for the 0.25 A source is

0.25 A.

We do know the 60 Ω Resistor has 15 V across it and therefore we can find the current through it from

This current goes from top to bottom, so the current in the 15 V source must split into

0.25 A down and 0.75 A to the right, so it must be the current in the 15 V source is 1.0 A.

The current through the 20 Ω resistor is 0.75 A joining with the 0.25 A current so the current is 1.0 A. This means the voltage across the resistor is

Now this resistor is in parallel to the 0.25 A source, so we know the voltage across the

0.25 A source must also be 20 V.

So since we have 1.0 A coming down the 20 Ω resistor and 0.25 A must go back to the

0.25 A source, so the 10 Ω resistor must have 0.75 A of current going through it. So the voltage across is

Since the 60 Ω Resistor has 0.25 A coming down and the 10 Ω Resistor has 0.75 A going left, they must add and then the current through the 15 V source must be 1.0 A. Finally doing a voltage walk around the middle loop and we have

Be careful of the polarities!

Which means

So putting these results in a table

Circuit Element	Voltage	Current
15 V Source	15 V	1.0 A
0.75 A Source	12.5 V	0.75 A
0.25 A Source	20 V	0.25 A
60 Ω Resistor	15 V	0.25 A
20 Ω Resistor	20 V	1.0 A
10 Ω Resistor	7.5 V	0.75 A

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This page last updated on January 14, 2019