Kirchhoff Junction Rule
Kirchhoff's current law is sum I = 0 at a node, using one consistent sign convention. It applies instantaneously when displacement or capacitor currents are represented appropriately.
Why this shows up in the exam
Finding unknown branch currents · Nodal circuit analysis · Checking a solved network
Learn the idea
Charge conservation requires the algebraic sum of currents at a node to be zero. A node cannot continuously store charge in a steady circuit. Whatever current flows in must flow out, with negative solved values simply indicating the true direction is opposite the guess.
🧠 Memory hook: No steady charge pile-up at a junction.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- sum I_in = sum I_out — steady-current node balance
- sum_k s_k I_k = 0 — algebraic node equation with chosen signs
How to approach it
- 1Assume branch directions
- 2Choose entering or leaving as positive
- 3Interpret negative results by reversing the arrow
Common slip-ups that cost marks
- •Changing sign convention mid-equation
- •Treating a negative answer as impossible
- •Writing redundant equations for every node
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A cell of emf 6 V and internal resistance 1 ohm is connected to a 2 ohm resistor. Find the circuit current.
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