What is Capacitor (Condenser)
A capacitor is a passive electronic component that stores an electric charge, a capacitor consists of two or more conducting plates separated by an insulating material called the dielectric. The dielectric must be a non conductive (insulating, opposes flow of electricity) material. There are several types of dielectrics such as paper, plastics, ceramic, glass, etc,use for making capacitor.
The capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance also depends on the dielectric constant of the substance separating the plates.
Capacitance is measured in Farads, named after Michael Faraday,This is a large unit, more common units are the microfarad, abbreviated µF (1 µF =10-6 ) and the picofarad, abbreviated pF (1 pF = 10-12 ).
1micro-farad (µF) = 10-6 farad
1micro-micro-farad (µµF) or picofarad (pF) = 10-12; farad
In this combination, the insulated plates of a number of capacitor are connected to one point M while all the earth–connected plates are joined to another point N. A source of electric charge is connected to the point M and the point N is ground (See Fig 2). In this arrangement, each capacitor has a potential difference V, but the charge will be distributed among them according to their capacitance .If the charges in the successive capacitor be Q1,Q2,Q3,etc, then the total charge Q=Q1+Q2+Q3+….(i)
Suppose, instead of the of the combination, a single capacitor of capacitance Cp be used such that same charge + Q given to the single capacitor produces a p.d. of V between its plates . The single capacitor, in this case, will be called an equivalent capacitor. For equivalent capacitor, therefore, Q= CpV. On the other hand, if C1, C2, C3... Etc be the capacitances of the individual capacitor of the combination, then we have, Q1=C1v ; Q2=C2V----etc. So according to the eqn. (i)
We have, Cp = C1 + C2 + C3 +------. i.e. the equivalent capacitance is sum of the individual capacitances.It is to be noted that due to parallel combination, the equivalent capacitance is greatly enlarge.
Ans. C = C1 + C2 + C3 ; C=3 + 10 + 15 ; C = 28mfd
The capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance also depends on the dielectric constant of the substance separating the plates.
Capacitance is measured in Farads, named after Michael Faraday,This is a large unit, more common units are the microfarad, abbreviated µF (1 µF =10-6 ) and the picofarad, abbreviated pF (1 pF = 10-12 ).
1micro-farad (µF) = 10-6 farad
1micro-micro-farad (µµF) or picofarad (pF) = 10-12; farad
Combination of capacitor:
When a number of capacitor are to be used together in a combination, it is known as “combination of capacitor”. All these capacitor combined together behave like a single capacitor, called the “equivalent capacitor. Capacitor can be combined in two ways: a) Series combination, b) Parallel combination
Series Combination:
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| Fig 1 (Series Combination) |
A number of capacitor are said to be connected in series if they are connected end to end consecutively (See Fig.1) is called Series Combination.If p.d.'s between the plates of the successive capacitor be V1, V2, V3 etc. and that between the plate A and G of the whole combination be V, then, V=V1 + V2 + V3 + ---------------------(a) suppose,instead of combination,a single capacitor of capacitance Cs is used such that the same charge+Q given to the single capacitor in this case, will be called an equivalent capacitor. For equivalent capacitor, V=Q/Cs.
On the other hand, if C1, C2, C3----etc. be the capacitance of the individual capacitors of the combination,then we have, V1=Q/C1 ; V2=Q/C2 etc.
So, according to the eqn.(a) we have 1/Cs =1/C1 + 1/C2 + 1/C3 + ---------.
i.e.the reciprocal of the equivalent capacitance is equal to sum of the reciprocal of the individual capacitance. It is to be noted that the equivalent capacitance in series combination is less then the capacitance of any individual capacitor of the combination but the series combination produces a high potential difference.
Ans. When connected in series, the equivalent capacitance C is 1/C =1/3 + 1/10 + 1/15. C = 2mfd.
Example:
Three capacitor of capacitance 3mfd, 10mfd and 15mfd are respectively joined in series,then what is the total capacitance?Ans. When connected in series, the equivalent capacitance C is 1/C =1/3 + 1/10 + 1/15. C = 2mfd.
Parallel combination
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| Fig.2 (Parallel combination) |
Suppose, instead of the of the combination, a single capacitor of capacitance Cp be used such that same charge + Q given to the single capacitor produces a p.d. of V between its plates . The single capacitor, in this case, will be called an equivalent capacitor. For equivalent capacitor, therefore, Q= CpV. On the other hand, if C1, C2, C3... Etc be the capacitances of the individual capacitor of the combination, then we have, Q1=C1v ; Q2=C2V----etc. So according to the eqn. (i)
We have, Cp = C1 + C2 + C3 +------. i.e. the equivalent capacitance is sum of the individual capacitances.It is to be noted that due to parallel combination, the equivalent capacitance is greatly enlarge.
Example:
Three capacitor of capacitance 3mfd, 10mfd and 15mfd are joined in parallel, (see Fig.2) then what is the total capacitance?Ans. C = C1 + C2 + C3 ; C=3 + 10 + 15 ; C = 28mfd
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