Science Buddies: "Ask an Expert"

Are there possibly more directions or advice on the assembly of the various pieces to this project? We have purchased exactly what was on the resource list, read the manual and are still having difficulty getting everything connected. We've enlarged the picture in the hopes to see what we've done wrong and still must not be connected correctly. Any guidance would be appreciated.

Unfortunately, you found a project that is lacking sufficient details for you to be able to reproduce it.

Part of publishing any scientific work is to provide sufficient details so that somebody else can reproduce your experiment. The author clearly failed.

So we have to look for clues....
Under Materials and Equipment
Optional: To get a more precise measurement of the light intensity, use an autoscaling digital multimeter for the readout. ... Set the multimeter to read DC (direct current) volts. Attach the two leads from the multimeter to the same output wires that go to the LED readout (springs 19 and 20).

Based on that, the "readout" on the schematic must be the equivalent of DC Volt meter. All DC Volt meters have TWO leads (+ and -). The schematic shows only one connection and it doesn't tell us if it is the + or - lead.

On the Background Tab
As the intensity of light increases, the resistance in the photoresistor decreases.

So the higher the intensity of the light, the lower the resistance of the photoresistor. At this point, we need to understand circuits. If you haven't researched Ohm's Law, you need to look it up so that you can follow my line of reasoning...

Assuming the potentiometer resistance is non-zero, the photoresistor and the potentiometer are in series. As the light increases, the total resistance decreases which means the current increases. The more current, the higher the voltage accross the potentiometer.

If we want the reading on the digital volt meter to increase with light intensity, we can measure the voltage across the potentiometer.
So...

The + lead of the DVM set to read DC volts needs to attach to the point shown on the schematic as the connection to the readout.
Because we want to measure the voltage accross the potentiometer, the - lead of the DVM (typically labeled "common") needs to be connected to the "gound" or - terminal of the battery.