In an electric circuit, a linear element is an electrical element with a linear relationship between input current and output voltage. The resistance, inductance or capacitance offered by an element does not change with the change in applied voltage or circuit current, the element is termed as linear element. Resistors are the most common example of a linear element; other examples include capacitors, inductors, and transformers.
Fundamentally nonlinear devices like transistors are often used to build approximately linear circuits. For example, an op-amp is designed to behave like a linear amplifier, as long as its input voltages remain within certain limits.