Science Buddies: "Ask an Expert"

How do you wire the volt meter and LED to a solar cell.

This depends somewhat on if you intend to have the voltmeter permanently hooked up to the circuit at the same time as the LED.

You can do a google, ask.com, or answers.com search on "voltmeter wiring", and LED wiring to get help on this. Also, there is useful info on "Solar Cell Wiring" to help you determine if series, parallel, or a series-parallel circuit is best for your project (you didn't state if you are using a single or multiple solar cells).

Do keep in mind that LEDs are diodes, and need to be hooked up with the correct polarity. No damage if hooked up backwards, but they won't light or pass any current. And in the same respect, the polarity of the voltmeter is important as otherwise it will deflect/read a negative voltage.

Hi jwbmbp,

What do you want to do with the voltmeter ? Remember that you measure voltage "ACROSS" two terminals as voltage is the difference in electromotive force between two different nodes.

Now both the solar cell and the LED are diodes. In the solar cell, it is a large p-n photodiode (diode that is special built to let light in and thus excite hole-electron pairs to form in the junction). The LED on the other hand is a diode made up certain semiconductor (like GaAs) that will emit light/photons during hole-electron pair recombination.
More on solar cells here:http://www.howstuffworks.com/solar-cell.htm
and LED here:http://en.wikipedia.org/wiki/LED

Now in order to hook up an LED across a voltage source you will need the to ensure that the LED does not conduct pass the maximum current allowed. You will need to obtain the datasheet for the LED that you are going to use. An example of a commonly used red LED is:
http://www.lumex.com/images/pdf/SSL-LX5093ID.pdf
It has a forward voltage Vf = 2V and peak current at 150mA.
So now you will need to insert a series resistor with the LED.
Say we pick 30mA current, and your solar cell produced Vs across it (which you measured with your voltage source). Then you would put a resistor = (Vs-Vf)/30mA.

So now you understand that LED need a current source to operate. And we made that by inserting the resistor in series with the LED.

By the way after reading the above you should realize that you need at least 2V across your solar cell(S) to even light up your LED. That is you may need to series your solar cells together.

Hope this helps. Good luck !