Example Data Table
| Method | Input Data | Formula | I3 Result |
|---|---|---|---|
| Node balance | Itotal = 12 A, I1 = 3.5 A, I2 = 4.25 A | I3 = Itotal - I1 - I2 | 4.25 A |
| Ohm law | V3 = 24 V, R3 = 8 ohm | I3 = V3 / R3 | 3 A |
| Power and voltage | P3 = 60 W, V3 = 12 V | I3 = P3 / V3 | 5 A |
| Charge and time | Q = 1800 C, t = 300 s | I3 = Q / t | 6 A |
| Current divider | Itotal = 10 A, R1 = 6 ohm, R2 = 3 ohm, R3 = 12 ohm | I3 = Itotal x G3 / Gtotal | 1.428571 A |
Formula Used
Node balance: I3 = Itotal - I1 - I2.
Ohm law: I3 = V3 / R3.
Power and voltage: I3 = P3 / V3.
Power and resistance: I3 = square root of P3 / R3.
Charge and time: I3 = Q / t.
Parallel divider: I3 = Itotal x (1 / R3) / ((1 / R1) + (1 / R2) + (1 / R3)).
How to Use This Calculator
Select the method that matches your known circuit data. Enter only the values required for that method. Choose correct units before solving. Press Calculate I3 to show the answer below the header and above the form. Use CSV or PDF buttons to export the same calculation result.
Understanding I3 Current in Electrical Circuits
I3 usually means the current in the third branch, third mesh, or third measured path of a circuit. The label depends on the diagram. The calculator treats I3 as an unknown current and solves it from the values you provide. This makes it useful for node checks, branch checks, and parallel load studies.
Why I3 Matters
Current balance is a core electrical idea. At a node, incoming current must equal outgoing current. If total current enters a junction, and two branch currents are known, the third branch current can be found by subtraction. This is a direct use of Kirchhoff current law. It is simple, but it is powerful.
Branch Current Methods
Some circuits give voltage and resistance instead of other currents. In that case, Ohm law is the best method. Divide branch voltage by branch resistance. If branch power is known, current can also be found from power equations. Use power divided by voltage when voltage is known. Use the square root relation when power and resistance are known.
Average Current
For batteries, capacitors, and charge flow problems, charge divided by time gives average current. This does not always describe every instant. It gives a useful overall value for a chosen time interval. Use seconds, minutes, hours, coulombs, amp hours, or milliamp hours carefully.
Parallel Divider Checks
In parallel circuits, lower resistance carries more current. The current divider option uses conductance. Conductance is the reciprocal of resistance. The branch conductance is compared with total conductance. That ratio tells how much total current flows through branch three.
Reading the Sign
A positive answer means I3 follows the selected reference direction. A negative answer means the real current flows opposite to that assumed arrow. This is not an error. It is useful information about actual circuit direction.
FAQs
1. What is I3 current?
I3 is commonly the current in the third branch, third mesh, or third labeled path of a circuit. Its exact meaning depends on the circuit diagram and reference arrow.
2. Which method should I choose?
Choose node balance when other branch currents are known. Choose Ohm law when voltage and resistance are known. Choose power methods when power data is available.
3. Why is my I3 result negative?
A negative result means the actual current direction is opposite to your selected reference direction. The magnitude is still useful for circuit analysis.
4. Can this calculator use milliamps?
Yes. Select mA as the input or output current unit. The calculator converts values internally before showing the final result.
5. What does the current divider option assume?
It assumes R1, R2, and R3 are connected in parallel and share the same voltage. It divides total current using branch conductance.
6. Can I use this for alternating current?
You can use it for simple resistive AC calculations. For impedance, phase angle, and reactive loads, use a phasor-based circuit method.
7. What units should resistance use?
You may enter ohm, kohm, or Mohm. Select the matching unit before calculating to avoid scaled results.
8. What is exported in CSV and PDF files?
The export includes the selected method, formula, entered values, calculated I3, and important notes from the result.