Teaching basic electricity - part 2.
In last month's newsletter, I mentioned having students use automotive bulbs to build and test basic circuits. Performing lab activities like these gives the students practice using a DMM, inspecting and testing bulbs, sockets, and wiring, and introduces troubleshooting procedures. And because of my sadistic nature, I mix blown bulbs and faulty sockets into the selection of parts the students use to build and test these circuits.
One of my favorite circuits uses an 1157 and a 194 bulb in series, shown in Figure 1. The students are told the 1157 bulb represents the brake or turn signal light and is supposed to illuminate. Of course the problem is the 1157 won't light up, shown in Figure 2. This usually makes the students try reversing the order of the bulbs and then assuming the 1157 bulb is "bad." I give the students spare bulbs and sockets so they can replace the "bad" bulbs with little effect.
After some more testing, circuit resistance and current flow as shown in Figures 3 and 4, students can see that the circuit is complete and neither bulb is "bad." Checking the voltage drop of the 1157, shown in Figure 5, begins to show why the circuit acts the way is does. I find this circuit is particularly effective in helping to teach voltage drop and the affect of unwanted resistance on circuit operation.
Another way to reinforce how voltage drops affect a circuit is to have students set up a series circuit with DMMs connected to show each voltage drop, shown in Figures 6 and 7. Figure 6 shows the voltage drop of each bulb, and Figure 7 shows each referenced to the battery. Again, having students set up and measure voltage drop this way can really reinforce what is going on in the circuit and creates a visual image in their heads about what voltage drop looks like.
Another benefit of using circuits and components such as those shown here is that as the connections and wires break, it automatically provides a supply of items that need repaired. This gives students practice cutting and stripping wire, installing terminals, and soldering pieces back together.
More to come next month.