According to Thevenin Theorem, a complex circuit is reduced to two resistor network, Thevenin Resistor, and Load resistor and a Thevenin Voltage source to avoid redundant computation to analyze a frequent changing resistor.
Gustav Kirchhoff was a German physicist, who presented two laws; Kirchhoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL). Ohm law is a very basic one, which may not be sufficient to analyze a complex circuit.
Mesh current Analysis provide a procedure for electric circuit analysis using mesh current as the circuit variable. The mesh analysis makes use of Kirchhoff’s Voltage Law as a basic key to analyze the circuit.