Electrical capacitance
“Electrical capacitance” :
some amount of charge given to the conductor when its size remain unchanged then the potential increases . it is clear that the amount of charge given to the conductor is directly proportional to the increase in potential.
i.e. Q α V
Or, Q = C.V--------(1)
where C is a proportionality constant which is known as capacitance of a conductor.
From eqn(1) [C = Q/V ]
*Definition:
Capacitance of a conductor is numerically equal to the charge required to raise the potential of conductor by unity (1 volt) .
* units of electrical capacitance ---
1) SI unit---coulomb/volt or farad(F)
2) CGS unit--- stat-coulomb/stat-volt
Or stat-farad.
*Dimensional formula of capacitance = [ M^-1L^-2T^4A^2 ]
*Relationship between farad and stat-farad:
By the definition :
Capacitance = charge/potential
Hence, 1 farad = 1coulomb/1volt
3×10^9 stat-coulomb
= ------------------------------
1/300 stat-volt
= 900×10^9 stat-farad
1 farad = 9×10^11 stat-farad
* Factor affecting the capacitance:
1) size of conductor :
on increasing the size of conductor the potential of a conductor decreases hence its capacity
(C = Q/V) increases.
2) presence of uncharged conductor near the charged conductor:
If an uncharged conductor is placed near a charged conductor then its potential decreases due to the following of charge from high potential to low potential and hence, capacity of charged conductor increases.
3) presence of other medium near the charged conductor:
If any dielectric medium is present near a charged conductor then the potential of charge conductor decreases. Hence, its capacitance increases by a factor K. (where k is the dielectric constant of a medium)
some amount of charge given to the conductor when its size remain unchanged then the potential increases . it is clear that the amount of charge given to the conductor is directly proportional to the increase in potential.
i.e. Q α V
Or, Q = C.V--------(1)
where C is a proportionality constant which is known as capacitance of a conductor.
From eqn(1) [C = Q/V ]
*Definition:
Capacitance of a conductor is numerically equal to the charge required to raise the potential of conductor by unity (1 volt) .
* units of electrical capacitance ---
1) SI unit---coulomb/volt or farad(F)
2) CGS unit--- stat-coulomb/stat-volt
Or stat-farad.
*Dimensional formula of capacitance = [ M^-1L^-2T^4A^2 ]
*Relationship between farad and stat-farad:
By the definition :
Capacitance = charge/potential
Hence, 1 farad = 1coulomb/1volt
3×10^9 stat-coulomb
= ------------------------------
1/300 stat-volt
= 900×10^9 stat-farad
1 farad = 9×10^11 stat-farad
* Factor affecting the capacitance:
1) size of conductor :
on increasing the size of conductor the potential of a conductor decreases hence its capacity
(C = Q/V) increases.
2) presence of uncharged conductor near the charged conductor:
If an uncharged conductor is placed near a charged conductor then its potential decreases due to the following of charge from high potential to low potential and hence, capacity of charged conductor increases.
3) presence of other medium near the charged conductor:
If any dielectric medium is present near a charged conductor then the potential of charge conductor decreases. Hence, its capacitance increases by a factor K. (where k is the dielectric constant of a medium)
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