# Homework Help: Simple Circuit with Two Sources

1. Apr 3, 2015

### showzen

1. The problem statement, all variables and given/known data

2. Relevant equations
KCL and KVL

3. The attempt at a solution
The sum of the currents at the top node equals the current out through the middle
(Call $I_1$ the current from the left and $I_2$ the right)

$I_3 = I_1+I_2$

And the sum of the voltages around the loops equals 0.

$-I_3(4k)-I_1(6k) + 10V = 0$

$-I_3(4k) + 4V = 0$

The system of equations yields solutions
$I_3 = 1mA$
$I_1 = 1mA$
$I_2 = 0$

Now, it appears that either I made a mistake, or there is zero current going through the source on the right. Is it logical to conclude that the source on the right is irrelevant to the circuit?

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2. Apr 3, 2015

### phinds

No mistake. Well, irrelevant to the circuit as drawn, yes; if other components were added it would likely come into play.

3. Apr 3, 2015

### showzen

Could I have predicted this from the start, and crossed off the right side source, and solved for just a single source with series resistors?

4. Apr 3, 2015

### SammyS

Staff Emeritus
That's difficult to say.

You might have noticed that removing the right side source & leaving that branch open would give a simple series circuit with the voltage across the 4kΩ resistor being 4 Volts.

That's not something one would normally look for.

Hindsight is wonderful.