Explanation:

Thevenin's theorem is a fundamental concept in circuit analysis, which states that any linear circuit with two terminals can be replaced by a single voltage source and a single series resistor. However, this theorem has some limitations, which are discussed below.

Linear Circuit:

A linear circuit is a circuit in which the output response is proportional to the input signal. Thevenin's theorem can be applied to linear circuits only. A linear circuit satisfies the principle of superposition, homogeneity, and additivity. These principles are necessary for the theorem to hold.

Active Circuit:

An active circuit is a circuit that requires an external power source to operate. An example of an active circuit is an amplifier. Thevenin's theorem can be applied to active circuits, provided they are linear.

Passive Circuit:

A passive circuit is a circuit that does not require an external power source to operate. An example of a passive circuit is a resistor. Thevenin's theorem can be applied to passive circuits, provided they are linear.

Nonlinear Circuit:

A nonlinear circuit is a circuit in which the output response is not proportional to the input signal. Thevenin's theorem cannot be applied to nonlinear circuits. Nonlinear circuits do not satisfy the principle of superposition, homogeneity, and additivity, which are necessary for the theorem to hold.

Conclusion:

Thevenin's theorem is an important concept in circuit analysis, which can be used to simplify complex circuits. However, this theorem has some limitations, which should be kept in mind while applying it to circuits. The theorem can be applied to linear circuits only, whether they are passive or active. Nonlinear circuits cannot be analyzed using the theorem.