Brief description

A capacitor (originally known as a condenser) is a passive two-terminal electrical component that stores electrical energy in an electric field. It consists of two electrical conductors separated by an insulator.

Use / Function

• Energy Storage: Temporarily storing charge for later release.
• Filtering: Smoothing out spikes in power supplies.
• Tuning: Used in circuits to select specific radio frequencies.
• Timing: In combination with resistors, creating precise time delays.
• Coupling/Decoupling: Allowing AC signals to pass while blocking DC.

Operating principle

A capacitor works by accumulating an internal charge.

1. Electric Field: When a voltage is applied across the two conductors (plates), an electric field develops across the insulator (dielectric).
2. Charge Accumulation: Positive charge builds up on one plate and an equal negative charge on the other.
3. Insulation: The dielectric prevents the charges from flowing between the plates, maintaining the potential difference.
4. Capacitance: The ability to store charge depends on the surface area of the plates, the distance between them, and the properties of the dielectric material.

How to create it

Simple Parallel Plate Capacitor

1. Conductive Plates: Two flat sheets of metal (like Tin foil or Aluminum foil).
2. Dielectric: A sheet of insulating material (like Paper, Glass, or even dry air).
3. Assembly: Sandwich the dielectric between the two metal plates. Ensure the plates do not touch each other directly.
4. Leads: Attach a Copper wire to each plate to serve as terminals.
5. Encapsulation: To improve durability and prevent moisture, the assembly can be dipped in melted Beeswax or resin.

Rolled Capacitor (More compact)

1. Lay down a long strip of foil.
2. Cover it with a slightly wider strip of waxed paper.
3. Lay another strip of foil on top.
4. Cover with another strip of waxed paper.
5. Roll the entire sandwich tightly into a cylinder and seal it.

Materials needed

• Conductors: Aluminum foil, Tin foil, or Copper sheets.
• Dielectrics: Paper (waxed or oiled), Glass, Ceramics, or Mica.
• Insulators/Sealants: Beeswax, paraffin, or resin.

Variants and improvements

• Leyden Jar: The earliest form, using a glass jar as the dielectric.
• Electrolytic Capacitor: Uses a chemical electrolyte to achieve much higher capacitance in a small volume (polarized).
• Variable Capacitor: Allows the overlap area of the plates to be adjusted, used for tuning Radios.

Limits and risks

• Breakdown Voltage: If the voltage is too high, it will arc through the dielectric, destroying the capacitor.
• Leakage: Over time, the stored charge will slowly leak away through the insulator.
• Polarity: Electrolytic capacitors can explode if connected with the wrong polarity.
• Safety: High-voltage capacitors can store a lethal charge even after the power is turned off. Always discharge them safely before handling.