Science Buddies: "Ask an Expert"

I tried to connect the circuit using the breadboard but the LED didn't glow. However when I didn't use the breadboard ( http://www.observationsblog.com/4/post/ ... -make.html) it glowed, I don't KNOW what's wrong, could it be the breadboard?

psain - Clearly there is a problem in using the breadboard, as you were able to get it to work wired directly. Are you following the instructions that came with the breadboard? There are rows of holes that are connected together, and adjacent rows that are insulated from other rows. The solderless breadboard makes it possible to easily join several wires together. Are you sure the 'gate' lead on the FET transistor is not touching anything else on the breadboard? Try another location on the breadboard and see if it operates with other rows and columns of connectors.

Rick Marz

Hello psain,

Please see this project description for more information.

As noted there,

"Field-effect transistors are normally on devices, meaning that with no negative electric field, they allow maximum current to flow. In the middle of the N-channel is a region of P-type semiconductor. Around the P-type material, there is a depletion zone. There are fewer electrons in the depletion zone, so the bigger the depletion zone is, the higher the resistance. In the presence of a negative electric field, the depletion zone gets bigger, the current is decreased, and so the LED on the circuit is turned off."

I think probably the gate had a negative charge when you first connected it. The LED came on after that charge had time to leak away. Try the detector after it has remained undisturbed for a while.

Good luck, WW

I tried all that and even got a new FET and it still doesn't work.

psain,

I performed this experiment and it worked as in the project description. Since there are many ways in which an experiment can fail, I can't pinpoint what's wrong with your setup. Here are a few ideas for testing

Check and double-check your circuit.

Be sure the battery is not dead.

Try a different transistor.

Review the project description to be sure you know what the circuit is supposed to do.

The breadboard is simply a convenient way to hoop up the circuit. If it works with another method of connecting the pieces, then use that method.

Good luck, WW