Monday, November 1, 2010

Posting six -- Current Electricity -- The Electrical Circuit

Today my grade nine applied science class performed an open ended lab on electrical circuits. We started by drawing a simple T-chart to list the symbols for the basic parts of a circuit (battery, wire, open and closed switch, light bulb, etc). We talked about how these symbols could be used by electricians anywhere to wire up a building, it didn’t matter what language they spoke the symbols would be the same.

1. Initiate and Plan = ENGAGE

I drew a super simple circuit diagram, using symbols, on the board and told the students to work in small collaborative groups build it.

I did not distribute any materials. I showed the students where all the materials were, in containers, on the side counter and told them to get what they needed. At first the students questioned how they were supposed to know what materials they needed. I simply told them to refer to their t-charts to decide what they should take from the bins. It took them about 20 seconds to figure it out!

The students investigated how to build the circuit and called me over to show me when the light bulb came on.

My second instruction to the students was to “construct at least four more working circuits and use the symbols to draw them”. Questions that were quickly asked, and answered, by the class included:

“How will we know if the circuits work?” “The light bulb will come on.”

“If we include a switch in our circuit should we draws it with the switch open or closed?” “Draw it both ways and then we will have two circuits done already!”

“What if the battery is dead?” “Then the light bulb won’t come on.”

“”How we will know if we blow the bulb?” “We will hear and see it pop.”

Really, the students did not need me. Together they had enough knowledge to perform the task perfectly. So I gave them some “special pink paper” to draw their circuits on and let them go to it.

2. Perform and Record = EXPLORE

The students designed a number of circuits. Interestingly, they were all series circuits. I thought that given enough time some might move onto parallel circuits. They enjoyed constructing the circuits and experimenting with various combinations of electrical equipment.

Safety note: The source of electricity was D cell batteries (1.5 volts, when new) and each group was limited to three of them so there was no danger of electric shock.

3. Analyze and Interpret = EXPLAIN

Although some of the students used the symbols correctly right from the start, to record their circuits, other students insisted on making artistic renditions of their circuits when instructed to draw them. When asked why they didn’t just use the symbols which were so much quicker and easier they replied “but I really like art.”

Others didn’t want to draw anything at all but when they realized how quickly they could sketch the symbols they decided it was easier to comply than to waste time arguing.

A few used the symbols correctly but drew their circuits as a straight line. When it was pointed out to them how the circuit actually went around in a continuous loop they quickly recognized the error of their ways and were pleased that it could quickly be corrected by drawing a wire from the end of the line around to the beginning rather than starting over from scratch.

4. Communicate = EXTEND

Once all the groups had built and drawn four circuits we discussed the problem of how to decide if it was the battery or the light bulb that was defective when a circuit was built correctly but didn’t work. This is when I introduced the voltmeter.

Without further instructions the class rushed to collect all the batteries out of the container and test them using the voltmeters (using instruments). This led to them discovering what to do if the voltmeter needle went in the wrong direction and what scale to choose on the voltmeter. Indeed five dead batteries were removed from the collection. When the students observed that I was asking them to give me the dead batteries and that I was placing them in a clean plastic jar rather than throwing them into the garbage they questioned me about this practise. This lead to some reflecting and explaining regarding the correct disposal of batteries and what would happen if they went to the landfill.

Once we had all decided that all the batteries were functional it was a natural progression to then test all the light bulbs. The next teacher to use our equipment will be very pleased – everything is fully functional and all the trouble shooting has been done for her!

How will I evaluate today’s lab? I collected the pink papers that the students had drawn their circuits on. This has provided me with documentation on their learning process.

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