Lesson Plan

• Recall Kirchhoff’s first law and state its mathematical form.
• Explain how the law follows from the principle of charge conservation.
• Apply the current law to determine unknown currents in simple circuits.
• Choose and justify a consistent sign convention for currents at a node.
• Solve circuit problems using the first law together with Ohm’s law.

• Projector or interactive whiteboard
• Printed circuit diagrams showing nodes
• Worksheet with practice problems
• Multimeter for a brief demonstration (optional)
• Calculator
• Whiteboard and markers

Begin with a quick demonstration of a simple three‑branch circuit on the board, asking students what happens to charge at the junction. Recall that they have previously studied charge conservation and current flow. Explain that today’s success criteria are to state Kirchhoff’s first law, link it to charge conservation, and use it to solve for unknown currents.

1. Do‑now (5 min): Short question on charge accumulation at a node – teacher checks responses.
2. Mini‑lecture (10 min): Present the statement and derivation of Kirchhoff’s first law from charge conservation, using a diagram of a node.
3. Guided practice (15 min): Work through the example procedure—identify a node, assign current directions, write the algebraic sum, and solve with Ohm’s law.
4. Collaborative activity (15 min): Pairs complete worksheet problems, choosing sign conventions and solving for currents while the teacher circulates.
5. Quick check (5 min): Exit ticket – write the law in words and give one real‑world example.
6. Summary (5 min): Recap key ideas and address any misconceptions.

Summarise that Kirchhoff’s first law is a direct expression of charge conservation at a node and that consistent sign conventions ensure accurate results. Students complete the exit ticket by writing the law and an example circuit. For homework, assign additional circuit problems that require applying the current law.