Electricity is a perfect example. We start with the basic concepts of voltage, current, resistance, and simple circuits. If you think of a simple balance beam with voltage in the middle – if resistance goes up, current goes down. Students can in fact understand how current, voltage and resistance are related without using any formulas. Similarly, you don’t have to bring in Ohm’s Law to understand the concepts of source, path, and load. In fact, I believe circuits are best approached at first without discussing Ohm’s Law. Students can build circuits and operate them to get a mental concept of how switches and loads behave. They can even build series and parallel circuits to see how they differ: all without formulas. Then AFTER the students understand the basic concept of an electrical circuit, you introduce Ohm’s Law as a mathematical description of a circuit. Now they have something real to relate to the parts of the formula and it is less abstract. You can even build circuits with heaters and take measurements to demonstrate how Ohms Law works.
After students have learned to solve Ohm’s Law problems, then we tell them that Ohm’s Law does not work in most AC circuits. At first, we don’t discuss the effects of alternating current, inductive, and capacitive reactance. It is just too much to take in at once. However, since these concepts have far more to do with most air conditioning circuits than Ohm’s Law, we can’t really afford to ignore them. The effect of inductive reactance can be demonstrated by operating a small motor in a circuit and comparing its resistance, current, and voltage. You can have students build circuits that demonstrate the effect of inductive and capacitive reactance and how they relate to each other. Depending on how much AC electricity you teach, you can put an oscilloscope on the circuits to show what happens in capacitive and inductive circuits (the teacher would be doing this.) Finally, you can bring in reactance and impedance calculations, although I must admit we do not have our Air Conditioning classes at Athens Tech doing LCR calculations. It’s a little like boiling a frog – you do it a little at a time. Before the students know it, they have learned some complex subject matter that would have sent them running for the exits if it had been presented all at once.