Electrolytic capacitors are polarized, which means the way that they are connected in a circuit matters. A 470 microfarad electrolytic capacitor is shown in the figure.
To tell which side is which, look for a large stripe or a minus sign (or both) on one side of the capacitor. The lead closest to that stripe or minus sign is the negative lead, and the other lead (which is unlabeled) is the positive lead. Another way to tell the sides apart is to look at the length of the leads. The shorter lead is the negative lead and the longer lead is the positive lead. If you clip the leads, you can still look for the stripe or minus sign.
The value of most electrolytic capacitors is marked on the case. Other types of capacitors are so small that there’s not enough room for the value, so manufacturers use a code. Don’t worry: You don’t need to know the capacitor code for the projects in this book because I tell you what to look for on the capacitors you use.
Note the value marked (and repeated) on the capacitor in the figure. This marking means that the capacitance is 470 microfarans and the maximum voltage that this capacitor should be exposed to is 25 V. This project uses a 9 V battery, so the 25 V rating is fine (and a capacitor rated for 16 V works fine, too). You should know that if you use a capacitor rated for a lower voltage than the power supply in your circuit, you risk damaging your capacitor.