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A fundamental electronic component that stores energy in an electric field, commonly used in filtering applications.

A capacitor is generally comprised of two conductive plates separated by a dielectric (non-conductive) gap. When a DC voltage is applied between the plates, an electrostatic field is generated, accumulating positive charge on one plate and negative on the other.

The schematic symbol for a non-polarized capacitor resembles the two-plate construction mentioned above:

Wikimedia capacitor symbol

The amount of charge that a capacitor can hold for a given voltage is referred to as its capacitance.

Capacitors block DC voltage (by charging up to the applied DC level) but conduct AC, with the voltage lagging the current by 90 degrees.

Key formulas:

  • Relationship of charge, capacitance and voltage: $$ Q = C \times V $$

  • Capacitive reactance: $$ X_C = \dfrac{1}{2 \pi f C} $$

  • Capacitor charging formula with series resistance R and applied voltage V: $$ V_C = V \times ({1 - e^{-\frac{t}{RC}}})$$

There are a variety of capacitor types, including:

  • electrolytic
  • ceramic
  • tantalum
  • polypropylene

Wikipedia article on capacitors