Capacitor Tutorial Summary

A capacitor consists of two metal plates separated by a dielectric.

  • 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-FaraduF ), nano-FaradnF ) and pico-FaradpF ) 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 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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  • C
    Colin Campbell

    Wayne, Do you have a tutorial on a DC cct describing the formulae for the charge &discharge current and voltage on an RC circuit?

  • R
    Robert Lyon

    Hi Wayne,
    Thanks for this excellent resource.
    Quick question.
    I’m planning to replace a couple non-polarized electrolytics in an old pair of Advents.
    researching the web, many people seem to think replacing these with metal film or poly non-electrolytics is a better way to go.
    Being a newbie, I don’t understand a lot of these finer points, but it’s my understanding that the electrolytics offer higher current capabilities as their main advantage. Soo, isn’t replacing them with non-electrolytics compromising the design?

    • Wayne Storr

      Hello Robert, Electrolytic capacitors have very high capacitance ratings for their physical size making them ideal for DC power supply reservoir and smoothing applications. However, standard electrolytics can create distortion when they are used for amplifier coupling and DC blocking circuits and also have much wider tolerances (+/-20%) than other capacitors. Replacing them with metallized film types is better if you can find them for your voltage and capacitance value, they are also self-healing so can handle surge currents better.

  • d
    domesh kumar

    When the negativ charge applied the first plate then shall we get the result

  • P
    Paul C

    Wayne, first of all, thanks for the wonderful series. I am a 30yrs old beginner in electronics, and this site is godsend to me; and your capacitor series is comprehensive but also easily grasped.

    Second, what I think Stevens was referring to:
    1: In a DC circuit, a plate will charge positive, and one negative. For electrolytic caps, they have to be properly placed so this takes place. For the rest, it doesn’t matter how you place them. When you discharge them, the charge will go (in conventional electronics) from the positive pole of the capacitor (corresponding with the positive pole of the battery) to the negative one, connected to ground.

    2: I have no idea about this description either. Resistance is resistance, and current is never constant, but depends on voltage and resistance – which for capacitors depends on the charge.

    3. A question of my own: What if, when touching a charged capacitor lead with a grounded metal object, you do not touch the other lead? You only ground ONE lead?

    Thanks again for the great articles!

    • Wayne Storr

      Regarding question 3. Capacitors store energy as a result of their ability to store an electrical charge. When connected to a supply, the resulting electron flow results in one plate of the capacitor holding a +ve charge while the other plate holds an equal and opposite -ve charge. As a result, the supply voltage uses energy to create and maintain the charge on the two plates with the amount of charge stored depending on the supply voltage applied to it. This charge creates an electro-static field across the dielectric that stores the energy between the plates of the capacitor. This energy can be regarded as potential energy.

      Assuming an ideal capacitor, when the supply voltage is removed, the capacitor maintains this charge indefinitely as it has nowhere else to go. However, if one leg or lead of the capacitor is grounded, there becomes an imbalance across the electric field causing the capacitor to discharge as the electro-static field looses energy.

  • M
    M. Stevens

    Couple ‘burning’ questions:
    1.) I understand the ‘purpose’ of electrolytic caps (what they do). But when non polarized caps become fully charged; then what? Where does it (Q) go when released?

    2.) As simple as Ohm’s Law is, I can’t understand why I keep reading about dropping current but not voltage drops in ‘capacative reactance’. Early on in electronics it’s repeatedly stressed that current is constant – does not change – so why are capacitors described as current resistors and voltage enhancers? What EXACTLY do they do? Purpose!?

    • Wayne Storr

      Regarding 1.) A capacitor stores energy on its two plates in the form of an electric field and it is the charge on the plates that forms the electric field. When current flows into a capacitor, charging it, the electric field becomes stronger, it stores more energy, and when current flows out of the capacitor, the voltage across its plates decreases and the strength of the electric field also decreases. The strength of the charging current is maximum when the two plates are uncharged. Then capacitors store energy as a result of their ability to store charge and the property of a capacitor to store this energy is called its capacitance. There is a direct relationship between capacitance, charge and voltage. A pure capacitor will hold its charge indefinitely, but in reality the DC or AC circuit in which a capacitor is connected will constantly charge and discharge it as the flow of electrical energy moves back and forth.

      Regarding 2.) I have never described capacitors as: “current resistors and voltage enhancers”. You need to ask this question to the person who refers to them as such.

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