In contrast to a practical voltage source, an imaginary deal source provide constant voltage regardless of load current because of no internal resistance. While ideal current source provides a constant current regardless of load current.

Star Delta Transformations and Delta Star Transformations allow us to convert resistances or impedances connected together at three different nodes from one type of connection to another and vice versa.

Maximum Power Transfer Theorem state that maximum power will transfer from source to load if and only if the load resistance is equal to source internal resistance. The theorem is purely about the transfer of power not efficiency.

Norton Theorem reduces any two port circuit to a Norton Resistor, a load resistor, and a current source in parallel. Where Thevenin Theorem incorporates voltage source in series.

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.

Resistors are said to be parallel if there is only one path for the flow of current. The total resistance in parallel is less than the individual resistors in parallel.

Fundamentals of Electric Circuits by Charles C. Alexandar and Mathew N. O. Sadiku is a textbook for electrical circuit analysis and design from beginner to advanced level.