In this lesson, students learn the applications of alternating current (AC) verses direct current (DC) and how to transition from AC to DC.

Students begin by using a variable power supply and an oscilloscope to evaluate their signals in the time domain. In the second part of the lesson students build half wave, full wave, and filtered rectifier circuits. An LED can even be substituted into the circuit to demonstrate one application where DC power is necessary (unless you want a flashing LED). The lesson and worksheet for this activity can be found here.

Full Wave Rectifier built by one of the students (Year 11) at the Wohl Reach Out Lab at Imperial College!

The beauty of this lesson is that students start with AC current, and then use a half wave rectifier to block charge from moving backward. They notice however that they lose half of the energy in the system and that the power supply is not constant. By then building a full wave rectifier they realize they can recover nearly all of the power; however, the supply is not constant. By adding in capacitors of varying size (capacitance) they are then able to smooth the signal into something resembling a DC supply, which is then used to power an LED.

Powering up the LED is certainly the highlight of the lesson for the students.

Voltage - time plots for the different power rectifiers