Capacitor Discharging pattern using LED

Components Required:

1) Breadboard

2) 470 ohm resistor

3) 1000uf Capacitor

4) LED (Any Color)

5) 9Volt Battery 

6) Push Button Normally Open (PBNO)

7) Digital Multimeter 

Procedure:

• Connect the circuit as shown in the circuit diagram below.

• The PBNO switch is normally open and the circuit is not closed therefore the capacitor will not be charged and the LED will not glow.

• Once the push button is pressed the charge flows from the battery and charges the capacitors and glows the LED.

• Even after the push button is released the LED glows for a period of 470 ms based on the RC time constant calculated for 1000uf capacitor and 470 ohm resistor. 

• Resistance value multiplied by the capacitance value gives the RC time constant.

• This is because when the push button is pressed the capacitor is charged and even after when the push button is released the charge stored in the capacitor closes the circuit and gets discharged through the closed circuit.

• Charge stored in the capacitor discharges exponentially which can be visually noticed by the brightness of the LED which becomes dimmer when discharging.

• To observe discharging pattern clearly use large resistance values say 10Kilo ohm for the same capacitance value which results in larger RC time constant for nearly 10 sec.

Circuit Diagram:

Figure 1: Capacitor Discharging pattern using LED Circuit simulation made in Multisim

Figure 2:  Capacitor Discharging pattern using LED (Push button open)

Figure 3:  Capacitor Discharging pattern using LED (Push button closed)