I wrote my book Easy Electronics to help beginners get acquainted with electronics more simply, quickly, and affordably than ever before. A dozen hands-on experiments show you the basics, and each one takes half an hour or less. You won’t need any tools at all.
You will need:
- AA batteries (3) with holder
- alligator jumper wires (3)
- 470µF capacitor
- 100µF capacitor
- 1kΩ resistor
- through-hole 5mm LED
- SPDT slide switch.
The type of capacitor shown here is called electrolytic. Its storage capacity, known as capacitance, is 470µF—but I’ll explain that in a moment. 50V is its maximum voltage, but for this experiment, a rating of 10V or higher is okay.
The short lead is the negative side, also identified with minus signs. That’s because this capacitor has polarity — never connect an electrolytic capacitor to a power supply the wrong way around.
Add the 1K resistor and the LED, with the negative side of the LED sharing the negative leg of the capacitor.
Now move the switch to the lower-right. The capacitor discharges itself through the LED.
Move the switch to the upper-left and wait 5 seconds for the capacitor to recharge. Now you can discharge it again and light the LED again!
HOW DOES IT WORK?
Inside the capacitor you used are two pieces of metal film known as plates. They are separated by paste called an electrolyte, which is why this capacitor is called electrolytic.
When electrons flow into one plate, they try to create an equal, opposite charge on the other. You can think of the plates as having positive and negative charges that attract each other.
The 1K resistor was needed because you charged the capacitor with 4.5V from the battery pack, and the LED can only handle about 1.8V. The resistor prevents the LED from being damaged.
The resistor also controls how fast the capacitor discharges. Substitute a 10K resistor (brown, black, orange) and the LED is dimmer than before and takes much longer to fade out.
Here’s another thing to try. Go back to using the 1K resistor. Remove the 470µF capacitor and substitute a 100µF capacitor. Push the switch to and fro, and now the LED lights up very briefly.
Electricity moves fast, but a capacitor and a resistor can make things happen slowly.
Capacitors such as the one shown above
are less than 1/2″ wide. They are dipped in a ceramic compound.
Most ceramic capacitors do not have polarity.
Many ceramic capacitors have a code printed on them instead of their actual capacitance.
Some ceramic capacitors are shaped like circular discs.
In simple circuits of the type you have been building, usually you can substitute a ceramic instead of an electrolytic if you wish. Note that for values around 10µF and above, ceramics may be more expensive.
Capacitance is measured in farads, abbreviated with letter F. But a 1F capacitor is very large. In hobby electronics we mostly use capacitors rated in microfarads, abbreviated µF. The µ symbol is the Greek letter mu, but often µF is printed as uF.
There are 1,000,000 microfarads in 1 farad, 1,000 nanofarads (nF) in 1 microfarad, and 1,000 picofarads (pF) in 1 nanofarad
There are two symbols for capacitors.
A polarized capacitor, such as an electrolytic, is on the left.
A nonpolarized capacitor, such as a ceramic, is on the right.
Some people use the symbol on the right everywhere in a schematic, and let you decide if you want to use an electrolytic capacitor, and if so, which way around it should be.
YOU MIGHT THINK:
A capacitor may seem similar to a battery. After all, they both store electricity.
A battery, however, uses chemical reactions, and even a rechargeable battery wears out after a limited number of charging and discharging cycles.
A capacitor does not use chemical reactions, and can still work as well after several years.
In this schematic showing the circuit that you just built, the double-throw switch has completed a circuit with the battery, so that the battery charges the capacitor.
In this schematic, the double-throw switch is in its other position, completing a circuit from one plate of the capacitor, through the resistor and the LED, back to the other plate.