CAPACITANCE
CAPACITANCE
WHAT IS A CAPACITOR??
A CAPACITOR ESSENTIALLY CONSISTS OF TWO CONDUCTING SURFACES SEPARATED BY A LAYER OF AN INSULATING MEDIUM CALLED DIELECTRIC. THE MAIN PURPOSE OF CAPACITORS IS TENDS TO STORE THE ELECTRICAL ENERGY BY AN ELECTROSTATIC STRESS IN THE DIELECTRIC.
CONDENSER
CONDENSER IS THE WORD THAT MEANS IT IS A MISNOMER SINCE A CAPACITOR DOES NOT (CONDENSE) ELECTRICITY AS SUCH IT RARELY STORES THE ENERGY...
WHAT DO YOU MEAN BY PARALLEL-PLATE CAPACITOR???
A PARALLEL PLATE MAY BE DEFINED AS THE PLATES PRESENTED THAT ONE PLATE IS JOINED TO THE POSITIVE END OF THE SUPPLY AND THE OTHER PLATE TO THE NEGATIVE END TO IT OR MAYBE GROUNDED OR EARTHED.
DURING AN EXPERIMENT IT IS POSES THAT THE WHEN THE PLATE B IS PRESENT WITH THE EARTHED THEN THE PLATE B IS MORE CAPABLE OF HOLDING MORE CHARGE WHEN B IS NOT THERE.
WHEN WE APPLY AN POWER SUPPLY WITH BATTERY ELECTRON FLOWS FROM A TO B. SO WHERE THE NEGATIVE CHARGED ELECTRON IS WITHDRAWN FROM A, THEN IT BECOME POSITIVE AND ELECTRON COLLECT ON B, IT BECOME NEGATIVE, SO THERE POTENTIAL DIFFERENCE DEVELOP BETWEEN THESE PLATES THOSE PLATES ARE A AND B.
CAPACITANCE
THE PROPERTY IN WHICH THE CAPACITOR TENDS TO STORE ELECTRICITY IS KNOWN AS CAPACITANCE. THE CAPACITANCE OF A CAPACITOR IS MAY DEFINED AS THE AMOUNT OF CHARGE REQUIRED TO CREATE A UNIT OF POTENTIAL DIFFERENCE BETWEEN ITS CAPACITIVE PLATES.
WE SUPPOSE Q COULOMB OF CHARGE TO ONE OF THE TWO PLATES OF CAPACITOR AND IF THE POTENTIAL DIFFERENCE OF VOLTS(V) IS ESTABLISHED BETWEEN TWO OF THEM THEN THE CAPACITANCE IS:--
ACCORDING TO FARADAY
C = Q/V = CHARGE/POTENTIAL DIFFERENCE
WHERE C IS EQUAL TO THE COEFFICIENT OF CAPACITANCE
THE PARALLEL PLATE CAPACITOR
A PARALLEL PLATE CAPACITOR CONSISTS OF TWO LARGE PLANE PARALLEL CONDUCTING PLATES SEPARATED BY A SMALL DISTANCE. ITS CAPACITANCE DEPENDS ON THE INTERVENING MEDIUM BETWEEN THE TWO PLATES.
CASE 1 PARALLEL PLATE CAPACITOR(AIR-FILLED)
WHEN A PARALLEL PLATE CAPACITOR JOINS WITH THE BATTERY THEN THE POSITIVE WILL CONDUCT AT ONE PLATE NEGATIVE CHARGE INDUCED AT SECOND PLATE. THIS RESULT IN A POTENTIAL DIFFERENCE BETWEEN THE 2 PLATES
V = POTENTIAL DIFFERENCE BETWEEN TWO PLATES
V/R=E
CASE 2 PARALLEL PLATE CAPACITOR (MEDIUM DIELECTRIC-FILLED)
ON FILLING A DIELECTRIC MEDIUM CAPACITANCE OF A CAPACITOR INCREASES K TIMES.
THIS WHOLE CONCEPT SHOWS CAPACITANCE DEPEND ON 3 MAIN FACTOR:-
1. MEDIUM
2. AREA OF THE PLATE
3. DISTANCE BETWEEN PLATES
CASE 3 PARALLEL PLATE CAPACITOR (HAVING CONDUCTING SLAB OF THICKNESS)
ON PLACING A CONDUCTING SLAB IN BETWEEN A 2 PLATE OF CAPACITANCE THE NET ELECTRIC FIELD INSIDE THE SLAB BECOME 0. THEREFORE THE ELECTRIC FIELD WILL LIE WITHIN THE DISTANCE OF (d-t)
COMBINATION OF CAPACITOR
WE CAN COMBINE SEVERAL CAPACITORS OF CAPACITANCE C1, C2, C3 -------Cn
TO OBTAIN A SYSTEM WITH SOME EFFECTIVE CAPACITANCE C.
TWO BASIC COMBINATIONS OF CAPACITORS ARE:-
1. SERIES COMBINATION
IN SERIES COMBINATION ALL THE CAPACITANCE (q=CONSTANT) ARE CONNECTED IN SUCH A WAY THE CHARGE REMAIN CONTACT THROUGH ALL THE CAPACITANCE.
PROPERTIES OF SERIES COMBINATION
1. CHARGE REMAIN CONSTANT
2. POTENTIAL DIFFERENCE DIVIDE AMONG EACH CAPACITANCE
3. NET CAPACITANCE ALWAYS DECREASE ACCORDING TO FORMULA:-
PROOF:- V=V1+V2+V3
Q/C=Q/C1+Q/C2+Q/C3
SERIES COMBINATION
1/C=1/C1+1/C2+1/C3 (CHARGE REMAIN CONSTANT)
PARALLEL COMBINATION
q= q1 + q2 + q3
CV= C1V + C2V + C3VNET:- C= C1+C2+C3
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