The input impedance and the output impedance are important and very useful concepts in circuit analysis, however students usually find it difficult to calculate and use them when it comes to specific electrical and electronic circuits. This difficulty mostly stems from the incomplete comprehension of the definition and the actual meaning of the input and output impedances as well as their association with Thevenin and Norton equivalent circuits.

To deal with the above issue, a two-hour lecture took place devoted to the presentation of the input and the output impedance to Electrical and Electronic Engineering students in the framework of a course on electronics. The lecture started with a definition of the two concepts given together with a general calculation formula. Then the input and the output impedance were associated with the Thevenin and Norton theorems and equivalent circuits as well as with the equivalent circuits for the four basic types of amplifiers (that is the voltage, transconductance, transimpedance and current amplifier). The lecture closed by asking the students to associate the above equivalent circuits and more specifically the input and output impedance with specific transistor amplifiers such as the common-emitter (CE), the common-collector (CC) and the differential amplifier.

Active participation of students was anticipated mainly regarding the revision of Thevenin and Norton equivalents (prior to the lecture) as well as with the calculation of the input and the output impedance for specific amplifier circuits part of which was presented in the classroom while the rest was given to students as homework with proper hints. Students’ active involvement was in any case necessary due to the teaching-time restrictions. The whole procedure was evaluated by means of a short questionnaire (distributed to the students following the lecture) that should be answered by means of a 5-grade Likert scale. Answers showed that students’ comprehension of the concepts of input and output impedances had been indeed enhanced.

Keywords: Engineering Education, Electrical Engineering Education, Electric circuits, Electronic circuits, Input impedance, Output impedance.