Consider a resistor connected to a variable voltage source. As the voltage is increased, the corresponding current value is recorded. The graphical representation reveals a linear relationship between the voltage and current. Such circuits where circuit parameters remain consistent despite changes in voltage or current are called linear circuits. Linear circuits are composed of linear elements or linear independent sources, and they satisfy homogeneity and additivity properties. This principle can help in circuit modeling to predict the source current when the voltage drop across the load changes. Initially, the current through the load resistor and the voltage drop across the top resistor are determined. Next, the voltage drop across the central branch is obtained, which is used to calculate the current through that branch. Applying KCL gives the total source current. When the load voltage changes, the new source current can be found by multiplying a constant with the old current and substituting the known values. However, the linearity principle does not apply to the power calculation, as power has a square dependence on the current.