After discussing the schematic and electric potential diagram assessment, we started a an activity that will last two or more days. It is a Circuits ILD. An ILD is an Interactive Lecture Demo. The instructional goals of the activity are to establish the relationships for current in series and parallel circuits. You know … current is constant in a series circuit (It=I1=I2=I3…) and the ‘junction rule’ for parallel circuits (It=I1+I2+I3..).
ILD’s are not really a new concept. I think this topic lends itself very well to an ILD. The Adv Phys Circuits ILD is a way for me to help the students learn the concepts without resorting to a lecture or a purely inquiry investigation. I have also found it really helps bring some common misconceptions about how current behaves to light (no pun intended this time). For example, take a look at circuit #1, many student think the current is the same because the resistors are the same size OR that the reading on A1 is the largest because it is the first one and the current has not “gone through” any resistors yet, making A3 the smallest because it has gone through two resistors. To check the first belief, circuit #2 adds a resistor and changes the value.
A really important aspect of the ILD (in my mind) is to actually check the values the students are predicting so they can see the results first hand.
So, here are some specifics about the set up and how I run it in my classes. The resistors in the ILD are bundles of christmas tree lights. Why these lights? Well, they are cheap and plentiful and they provide a visual for the students as we check them. The source is simply a 9v battery. Here is a picture of one of the circuits set up and ready to check:
In class, I put the students into groups of three based on the results of some recent assessments. I put a green, a yellow and a red (see this post of the info on these colors) if possible. I hand out each circuit one at a time and have the groups discuss and make predictions on a big WB. When all the groups are ready, we hang the boards, discuss a bit then actually check the values as shown above. I do not explain the ‘why’ this is the answer until after a few circuits have been worked through. I want the students to come up with some ideas to base the predictions on, then allow them to check it with the next circuit. If I sense that things are going south or the students are getting really frustrated because they are not catching on, then I might provide some small group ‘hints’ as I am walking around. Some years we even turn it into a competition.. wich group gets the most predictions correct. More tomorrow about the remaining circuits.
Today was the WB’ing of the Ohm’s Law experiment. We followed the same basic process with this group that we did with the advanced group. There was one slight change… to see if the material makes a difference, I had the students use the DMM to check the resistance of the ‘sister spool’ from a different set of spools. The set we used in the experiment was Ni-Cr, and the other (older) set is NS.