Electricity+and+electromagnetism


 * Electricity and electromagnetism**

Existing course days: Day 8: Electricity 1 Day 14 Electromagnetism Day 24 - DC circuit theory Day 25 - Exponential processes. Day 27 - Fields - gravitational and electrical

Looking at the list above I can't believe how little time we spent on this.

First and foremost, students need a firm grasp of the fundamentals. Too few teachers relate students ideas about electricity to their ideas on atomic structure. Common misconceptions about electricity are much more easily dispelled if they produce conflict with other accepted models. It's difficult to build a sound model of what's going on in a circuit without getting the fundamentals right. Modelling is vital - use the IOP rope model of a circuit. As ever, when a model is used, make sure that your students engage with it critically - ask them to think where the model explains things well and where it is in danger of breaking down. Be aware that there is a danger of losing sight of the wood for the trees with models.
 * Fundamental models.**

Practical activities that involve building and testing circuits are the bane of some teachers' lives. The advice form 'Getting Practical' is invaluable: before you wade into a set of practical activities, ask yourself why the students are doing what they do. Is it getting the point across effectively? Are they learning what they should or simply struggling with inappropriate equipment? If the purpose of the activity is to get a set of current readings at different positions in a parallel circuit, is fifteen minutes spent making, cocking-up, remaking the circuit, then testing and replacing a series of blown bulbs actually time well spent? Would it make more sense to have half a dozen circuits made up on a bit of MDF and put the activity into a circus? There is something to be learned from problem circuits; make it a deliberate activity - introduce a lesson on trouble shooting circuits, it's a useful skill and will increase students' confidence.
 * Circuit practicals**

One of the areas that gives students the greatest degree of difficulty is the idea of energy in series circuits; the question "How does the electricity //know// how much energy to give each bulb?" comes up all the time. Keep referring back to the rope model - it works a treat for this one. Increasing resistance at one point in the circuit slows the flow of electrons for the whole circuit, so less energy is transferred in every part of the circuit. Even experienced physicists have trouble with these concepts sometimes! I was asked a while ago by a physics teacher of ten years experience how electrons could lose energy in one part of a series circuit and still maintain the same drift velocity as the rest of the current - basically wanting to know how the charge could have the same speed in and out of a bulb (ergo ,same current) if some energy was being lost. Stuck? Imagine a boy falling from a tree. Let's say it's the ugly tree and he hits every branch on the way down. (I taught in Gloucestershire). Gravity accelerates the boy. He hits a branch and transfers some energy to it. He loses a little downward speed. Because he is still in a gravitational field he is accelerated again until he hits the next branch. Similarly, when you put a voltage across a bit of wire, an electric field is produced that accelerates electrons. Depending on the resistance of the circuit, they will reach a sort of terminal speed (drift velocity) relatively quickly. If energy is transferred in a bulb filament or other component then the electrons that transfer that energy are still in the electric field and still get accelerated.
 * Tricky concepts.**