Lets know about Capacitor Because Capacitor is a important Element in The Electrical Basics
◆Capacitor :
A capacitor essentially consists of two conducting surfaces separated
by a layer of an insulating medium called dielectric. The conducting surfaces may be in the form of either circular (or rectangular) plates or be of
spherical or cylindrical shape. The purpose of a capacitor is to store electrical energy by electrostatic stress in the dielectric (the word ‘condenser’
is a misnomer since a capacitor does not ‘condense’ electricity as such, it
merely stores it).
A parallel-plate capacitor is shown in Fig. One plate is joined to
the positive end of the supply and the other to the negative end or is earthed.
It is experimentally found that in the presence of an earthed plate B, plate
A is capable of withholding more charge than when B is not there. When
such a capacitor is put across a battery, there is a momentary flow of
electrons from A to B. As negatively-charged electrons are withdrawn
from A, it becomes positive and as these electrons collect on B, it becomes
negative. Hence, a p.d. is established between plates A and B. The transient
flow of electrons gives rise to charging current. The strength of the charging
current is maximum when the two plates are uncharged but it then decreases and finally ceases when
p.d. across the plates becomes slowly and slowly equal and opposite to the battery e.m.f.
◆Capacitance :
The property of a capacitor to ‘store electricity’ may be called
its capacitance.
As we may measure the capacity of a tank, not by the total
mass or volume of water it can hold, but by the mass in kg of
water required to raise its level by one metre, similarly, the
capacitance of a capacitor is defined as “the amount of charge
required to create a unit p.d. between its plates.”
Suppose we give Q coulomb of charge to one of the two plate
of capacitor and if a p.d. of V volts is established between the two,
then its capacitance is
C = Q/V
Capacitance = Charge/Potential Difference
Hence, capacitance is the charge required per unit potential difference.
By definition, the unit of capacitance is coulomb/volt which is also called farad (in honour of
Michael Faraday)
∴ 1 farad = 1 coulomb/volt
One farad is defined as the capacitance of a capacitor which requires a charge of one coulomb
to establish a p.d. of one volt between its plates.
One farad is actually too large for practical purposes. Hence, much smaller units like microfarad
(μF), nanofarad (nF) and micro-microfarad (μμF) or picofarad (pF) are generally employed.
1 μF = 10−9 F; 1 nF = 10−9 F ; 1 μμF or pF = 10−12F
Incidentally, capacitance is that property of a capacitor which delays and change of voltage
across it.
◆Capacitor :
A capacitor essentially consists of two conducting surfaces separated
by a layer of an insulating medium called dielectric. The conducting surfaces may be in the form of either circular (or rectangular) plates or be of
spherical or cylindrical shape. The purpose of a capacitor is to store electrical energy by electrostatic stress in the dielectric (the word ‘condenser’
is a misnomer since a capacitor does not ‘condense’ electricity as such, it
merely stores it).
A parallel-plate capacitor is shown in Fig. One plate is joined to
the positive end of the supply and the other to the negative end or is earthed.
It is experimentally found that in the presence of an earthed plate B, plate
A is capable of withholding more charge than when B is not there. When
such a capacitor is put across a battery, there is a momentary flow of
electrons from A to B. As negatively-charged electrons are withdrawn
from A, it becomes positive and as these electrons collect on B, it becomes
negative. Hence, a p.d. is established between plates A and B. The transient
flow of electrons gives rise to charging current. The strength of the charging
current is maximum when the two plates are uncharged but it then decreases and finally ceases when
p.d. across the plates becomes slowly and slowly equal and opposite to the battery e.m.f.
◆Capacitance :
its capacitance.
As we may measure the capacity of a tank, not by the total
mass or volume of water it can hold, but by the mass in kg of
water required to raise its level by one metre, similarly, the
capacitance of a capacitor is defined as “the amount of charge
required to create a unit p.d. between its plates.”
Suppose we give Q coulomb of charge to one of the two plate
of capacitor and if a p.d. of V volts is established between the two,
then its capacitance is
C = Q/V
Capacitance = Charge/Potential Difference
Hence, capacitance is the charge required per unit potential difference.
By definition, the unit of capacitance is coulomb/volt which is also called farad (in honour of
Michael Faraday)
∴ 1 farad = 1 coulomb/volt
One farad is defined as the capacitance of a capacitor which requires a charge of one coulomb
to establish a p.d. of one volt between its plates.
One farad is actually too large for practical purposes. Hence, much smaller units like microfarad
(μF), nanofarad (nF) and micro-microfarad (μμF) or picofarad (pF) are generally employed.
1 μF = 10−9 F; 1 nF = 10−9 F ; 1 μμF or pF = 10−12F
Incidentally, capacitance is that property of a capacitor which delays and change of voltage
across it.
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