Circuit Laws: Kirchhoff’s Law & Network Theorems

Understanding basic electrical circuit laws for exams and practical use

🔌 Kirchhoff’s Laws

1. Kirchhoff’s Current Law (KCL)

KCL states that the total current entering a junction equals the total current leaving the junction.
Formula: ∑ I_in = ∑ I_out
This is based on the law of conservation of charge.
Example: If 3A and 2A enter a node, and 4A leaves, the remaining 1A must also leave. ✅

2. Kirchhoff’s Voltage Law (KVL)

KVL states that the sum of voltages in any closed loop of a circuit is zero.
Formula: ∑ V = 0 (around a loop)
This is based on conservation of energy.
Example: Battery = 12V, Resistors drop 5V and 7V → 12 - 5 - 7 = 0 ✅

📘 Network Theorems

1. Ohm’s Law

Defines the relationship between Voltage, Current, and Resistance.
Formula: V = I × R

2. Thevenin’s Theorem

Simplifies a complex circuit to a single voltage source and series resistance.
Use: Helpful for analyzing load variations.

3. Norton’s Theorem

Simplifies a circuit to a current source and parallel resistance.
Note: Can convert between Thevenin and Norton.

4. Superposition Theorem

In circuits with multiple sources, consider one source at a time.
Replace other sources: Voltage → short circuit, Current → open circuit.

5. Maximum Power Transfer Theorem

Maximum power is delivered when Load Resistance = Source/Internal Resistance.
Formula: R_L = R_th