Capacitors in a Circuit

Exercise Seven: Capacitors and Push Buttons

Background Knowledge:

How to draw a Schematic
Resistors, Push Buttons, Capacitors, and LEDs
How to read and use a Multimeter
Current Flow in a Series Circuit and Parallel Circuit
Ohm's Law and Power

What you'll need:

1 - 9 Volt Battery

1 - 9 Volt Battery Harness

1 - Breadboard

1 - 1N4007 Rectifier Diode

1 - Momentary PBNO

1 - Momentary PBNC

1 - 470-Ohm 1/4 Watt THR

1 - 2.2 uF 35V Radial Capacitor

1 - 10 uF 35V Radial Capacitor

1 - 100 uF 35V Radial Capacitor

1 - 470 uF 35V Radial Capacitor

1 - 1000 uF 35V Radial Capacitor

1 - Red 5mm LED

Capacitors are electronic components that store electrical energy in an electric field. They consist of two conductive plates separated by an insulating material called a dielectric. The conductive plates can be made of metal, such as aluminum or tantalum, and the dielectric can be made of various materials, such as ceramic, paper, or plastic.

When a voltage is applied to a capacitor, electrons accumulate on one plate, while an equal number of electrons are repelled from the other plate, creating an electric field between them. The capacitance of a capacitor is a measure of its ability to store electrical charge, and it depends on the area of the plates, the distance between them, and the type of dielectric material used.

How it works:

The normally open push button closes.
Voltage fills the capacitor and powers the LED.
The PBNO opens, cutting off the voltage.
The capacitor drains through the LED.

As the capacitor drains, the voltage decreases.
As the voltage decreases, the LED dims.

Note* The Red dotted line in this schematic just represents a wire that you will remove and replace later. *

https://www.falstad.com/circuit/

Look closely at the electrolytic capacitors. Be sure to note the stripe and the short leg that marks the polarity. Build your first circuit for this experiment with a 2.2 uF capacitor.

Steps:

When you build it, consider and reflect on what happens in your circuit as you push the button then let go.

Draw the schematic diagram and label the components.

When labeling your components in a circuit each resistor will be R#, so in this circuit R1, R2, R3, and R4. R1 will typically be the resistor closest to the positive node.
Your circuit should also have the nominal values of each component annotated on the schematic diagram.
- With Resistors, you can find this using the Resistor Color Codes.
- With polarized radial capacitors, the nominal value should be written on the casing.
Using what we know about current, you should also label the schematic with the anticipated current flow direction.

Disconnect the wire represented by the red dotted line between the capacitor and R1.

Push the button to charge the capacitor.

Set your multimeter to the proper voltage range.

Put the red probe to the positive side of the cap, and the black to the ground. Record the voltage that first appears. The capacitor will slowly leak through the multimeter.

Reconnect the wire and pay attention to what happens on your multimeter.

What is happening and why?

Use the table to record your information as you experiment with the circuit.

As you replace each capacitor, record the time the LED stays on.
Be sure to hold the PBNO on for at least a few seconds or so to make sure the capacitor is full.

Questions:

Describe the pattern you see here. Why does the pattern form?
Briefly describe what capacitors do.
Why would we never want to fool around with capacitors?

*Extra Experiment: Place the 1000uF capacitor back into its original position. Now replace the normally open push button (PBNO) with the normally closed push button (PBNC). Describe the action of this circuit.*

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