currentohms-lawparallel
I am trying to find all currents in this circuit:
(Question 19 from https://www.allaboutcircuits.com/worksheets/algebraic-equation-manipulation-for-electric-circuits/)
Although I'm familiar with Ohm's law and can find values in series-parallel circuits, I don't know how to approach this.
What is the meaning of the circle with arrow in it symbol, that has 5mA?
Should I interpret that as an extra power source? Why not use a battery symbol there then?
What is the approach to solve this problem?
The easiest way to do this is to use superposition. Set one source to \$0\$ (i.e. shorted) and find the node voltage due to the other source, then set the other source to \$0\$ and find the node voltage due to the first source. Add the two contributions for the node voltage due to both sources.
For the case with the \$14\$V source set to \$0\$ (finding the contribution of the \$15\$V source) the circuit looks like this:
simulate this circuit – Schematic created using CircuitLab
\$R_2\$ and \$R_3\$ are in parallel since \$V_2\$ is shorted, and \$V_x\$ can be found using a simple voltage divider:
$$V_x = \frac{R_2||R_3}{R_2||R_3 + R_1}15\text{V}$$
It's a similar process for finding \$V_y\$, the contribution of the \$14\$V source to the node voltage (with the \$15\$V source set to \$0\$).
Then by superposition $$V_{\text{NODE}1} = V_x + V_y$$
The current direction on the diagram is supposed to be the right answer
The current direction in the diagram is the WRONG answer.
If you combine those two resistors into a single 100kohm resistor, current flows from the higher potential to the lower potential and the amount is the potential difference (20V-10V) divided by 100kohm i.e 100 micro amps flow from right to left thru the resistor.
Best Answer
It's a constant current source - it draws a constant 5 mA come what may.
You should interpret that as a current source - it can be converted to a voltage source in series with a resistor if that might help you - look up Thevenin equivalent sources: -