Capacitor Tutorial Summary

Table of Contents

Capacitors are energy storage devices which have the ability to store an electrical charge across its plates. Thus capacitors store energy as a result of their ability to store charge and an ideal capacitor would not loose its stored energy.

The simplest construction of a capacitor is by using two parallel conducting metal plates separated through a distance by an insulating material, called a the dielectric as summarised below.

  • A capacitor consists of two metal plates separated by a dielectric.
  • The dielectric can be made of many insulating materials such as air, glass, paper, plastic etc.
  • A capacitor is capable of storing electrical charge and energy.
  • The higher the value of capacitance, the more charge the capacitor can store.
  • The larger the area of the plates or the smaller their separation the more charge the capacitor can store.
  • A capacitor is said to be “Fully Charged” when the voltage across its plates equals the supply voltage.
  • The symbol for electrical charge is Q and its unit is the Coulomb.
  • Electrolytic capacitors are polarized. They have a +ve and a -ve terminal.
  • Capacitance is measured in Farads, which is a very large unit so micro-Farad ( μF ), nano-Farad ( nF ) and pico-Farad ( pF ) are generally used.
  • Capacitors that are daisy chained together in a line are said to be connected in Series.
  • Capacitors that have both of their respective terminals connected to each terminal of another capacitor are said to be connected in Parallel.
  • Parallel connected capacitors have a common supply voltage across them.
  • Series connected capacitors have a common current flowing through them.
  • Capacitive reactance, XC is the opposition to current flow in AC circuits.
  • In AC capacitive circuits the voltage “lags” the current by 90o.

The basic construction and symbol for a parallel plate capacitor is given as:

capacitor tutorial the symbol


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