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Electronics Projects: Charging and Discharging a Capacitor

One of the most common uses for capacitors in an electronic circuit is to store a charge that you can discharge when it's needed. Project 3-1 presents a simple construction project on a solderless breadboard that demonstrates how you can use a capacitor to do this.

You connect an LED to a 3 V battery power supply and use a capacitor so that when you disconnect the battery from the circuit, the LED doesn't immediately go out. Instead, it continues to glow for a moment as the capacitor discharges.

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Here are some additional points you might want to ponder or things you might want to try after you complete Project 3-1:

  • Pull the LED out of the breadboard, and then close the switch to charge the capacitor. After a few seconds, open the switch. Then, use the voltmeter function of your multimeter to measure the voltage across the two leads of the capacitor. Notice that even though the battery is disconnected from the circuit, the capacitor reads 3 V.

  • Try varying the size of the capacitor to see what happens. If you use a smaller capacitor, the LED extinguishes more quickly when you remove the power. If you use a larger capacitor, the LED fades more slowly.

  • You may not be able to find a capacitor larger than 1,000 μF, but you can increase the capacitance by adding more capacitors in parallel with the 1,000 μF capacitor.

  • Try adding a resistor in series with the capacitor. To do that, simply replace the jumper wire you connected in Step 6 with a resistor.

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