A capacitor (originally known as condenser) is a passive two-terminal electrical component used story energy in its electric field.

when an electrical device is connected across battery an electrical field develops across the stuff, inflicting electric charge +Q to gather on one plate and charge -Q to gather on the opposite plate.

  • A basic capacitance has 2 parallel plates separated by AN insulation.
  • A capacitance stores AN electrical charge between the 2 plates.
  • The unit of capacitance is Farads (F).
  • Capacitance values square measure commonly smaller, such as µF, nF or pF.


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What is a capacitor?

Take 2 electrical conductors (things that permit electricity flow through them) associated separate them with a material (a material that does not let electricity flow terribly well) and you create a capacitor: one thing that may store current. Adding current to an electrical condenser is termed charging; emotional the energy from an electrical condenser is thought as discharging.

There unit of measurement many alternative kinds of electrical devices on the market from very very little condenser beads used in resonance circuits to large power issue correction capacitors, however, all of them do an identical issue, they store charge. Capacitance is effectively the pliability to store charge. In its simplest sort, associate degree device consists of two parallel plates. it’s found that after battery or the opposite voltage provide is connected to the two plates as shown a current flows for a short time associate degreed one plate receives a way more than electrons, whereas the other has too few. throughout this way, one plate, the one with the excess of electrons becomes charged, whereas the other becomes charged.

FIg: Capacitor symbol

How can we increase the capacitance?

It’s intuitively obvious that if you create the plates larger, you will be able to store additional charge (just as if you create a closet larger you’ll be able to stuff additional things within it). thus increasing the world of the plates additionally will increase the capacitance. Less clearly, if we have a tendency to scale back the gap between the plates, that additionally will increase the capacitance. that is as a result of the shorter the gap between the plates, the additional result the plates wear each other. The second plate, being nearer, reduces the potential of the primary plate even additional, which will increase the capacitance.

The final factor we have a tendency to factor we are able to do to extend the capacitance is to alter the material (the material between the plates). Air works practically, however different materials square measure even higher. The glass is a minimum of five times simpler than air, that is why the earliest capacitors (Leyden jars, mistreatment normal glass because the dielectric) worked thus well, however it’s significant, impractical, and arduous to squeeze into tiny areas. waxed paper is regarding four times higher than air, very thin, cheap, straightforward to create in massive items, and simple to roll, that makes it a wonderful, sensible material. the most effective material materials square measure product of polar molecules (ones with a lot of positive charge on one facet and a lot of negative charge on the other). after they sit within the force field between 2 condenser plates, they line up with their charges inform opposite to the sphere, that effectively reduces it. That reduces the potential on the plates and, as before, will increase their capacitance. in theory, water, that is formed of very small polar molecules, would create a wonderful material, roughly eighty times higher than air. much, though, it isn’t thus sensible (it leaks and dries out and changes from a liquid to ice or steam at comparatively modest temperatures), thus it isn’t utilized in real capacitors.

Basic capacitor construction

Storing a charge between the plates

  • Electrons on the left plate square measure attracted toward the positive terminal of the voltage supply.
  • This leaves associate degree more than charged holes.
  • The electrons square measure pushed toward the correct plate Excess electrons leave an electric charge.

Types of capacitors

  1. The dielectric material determines the type of capacitor.
  2. Common types of capacitors are:
  • Ceramic

  • Plastic film

  • Mica

Some capacitors area unit polarised, they’ll solely be connected a way around.
Electrolytic capacitors area unit polarised.

  •  Variable capacitors square measure employed in facility, radios, televisions, and VCRs.
  •  They will be adjusted by shoppers by standardization controls.
  • Trimmer’s square measure internal changed capacitors that a shopper cannot adjust.
  • These variable capacitors would be tough to squeeze into your mobile and iPod
  • Current technology uses semiconductor variable capacitors referred to as varactors ( varicaps )

Standard Units of Capacitance

  1. Microfarad  (μF)   1μF = 1/1,000,000 = 0.000001 = 10-6 F
  2. Nanofarad  (nF)   1nF = 1/1,000,000,000 = 0.000000001 = 10-9 F
  3. Picofarad  (pF)   1pF = 1/1,000,000,000,000 = 0.000000000001 = 10-12 F