Capacitors and Capacitance – Notes

Electrical Engineering » Notes » Capacitors and Capacitance


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 property of a capacitor to ‘store electricity’ may be called its capacitance.

The capacitance of a capacitor is defined as the amount of charge required to create a unit potential difference between its plates.

Suppose we give Q coulomb of charge to one of the two plate of capacitor and if a potential difference of V volts is established between the two, then its capacitance is :

C = Q/V = charge / potential differnce

Hence, capacitance is the charge required per unit potential difference.

By definition, the unit of capacitance is coulomb/volt which is also called farad.

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 potential difference 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 picofarad (pF) are generally employed.

1 μF = 10-6 F
1 nF = 10-7 F

1pF = 10-12 F

Capacitors in Series

C1, C2, C3 = Capacitances of three capacitors
V1, V2, V3 = p.ds. across three capacitors.
V = applied voltage across combination
C = combined or equivalent or joining capacitance.
In series combination, charge on all capacitors is the same but p.d. across each is different.

1/= 1/1/1/3

Capacitors in Parallel

= + C­+ C­3

Energy Stored in a Capacitor

On charging the capacitor, the electrostatic field set up in the dielectric medium store energy. On discharging the capacitor, the field collapses and the stored energy is released.

1/2 (CV2) joules  = 1/2 (QV) joules = Q2/2joules

C capacitance in farads and
V =  voltage in volts.

Current-Voltage Relationships in a Capacitor

The charge on a capacitor is given by the expression Q = CV. By differentiating this relation, we get :

i = dQ/dt = d (CV)/dt = C dv/dt

Capacitors and Capacitance – Mcq
Capacitors and Capacitance – Notes
Capacitors and Capacitance – IQ
Subject Name : Electrical Engineering
Posts Name : Assistant Engineer, Management Trainee, Junior Engineer, Technical Assistant
Electrical Engineering Books

Objective Electrical Technology (6500+ Objective Questions...
V.K Mehta (Author); English (Publication Language); 1089 Pages - 11/30/2004 (Publication Date) - S Chand (Publisher)
₹ 630
An Integrated Course in Electrical Engineering
J.B. Gupta (Author); English (Publication Language); 1100 Pages - 01/01/2013 (Publication Date) - S.K. Kataria & Sons (Publisher)
₹ 1,112
Basic Electrical Engg
Binding: paperback; Language: english; This product will be an excellent pick for you; V.K Mehta (Author)
₹ 813
Product Condition: No Defects; Kulshreshtha D (Author); English (Publication Language); 880 Pages - 07/01/2017 (Publication Date) - McGraw Hill Education (Publisher)
₹ 420
A Handbook for Electrical Engineering(Old Edition)
ME Team (Author); English (Publication Language); 692 Pages - 01/01/2015 (Publication Date) - Made Easy Publications (Publisher)
₹ 210

GATE 2023 Total InfoENGG DIPLOMAUGC NET Total Info
IES 2023 Total InfoPSUs 2022 Total InfoCSIR UGC NET Total Info
JAM 2023 Total InfoM TECH 2023 Total InfoRAILWAY 2022 Total Info

Related Posts

  • Feeder Protection - 5Feeder Protection » Exercise - 1 5. The term backlash is associate with : (a) Servomotors (b) Induction relays (c) Gear Trans (d) Any of the above
    Tags: electrical, engineering
  • Transformer - 1Transformer » Exercise - 1 1.  A transformer transforms : (a) frequency (b) voltage (c) current (d) voltage and current
    Tags: electrical, engineering
  • Servomotors – 2Servomotors » Exercise - 12. One of the basic requirements of a servomotor is that it must produce high torque at all : (a) loads (b) frequencies (c) speeds (d) voltages
    Tags: electrical, engineering
  • Synchros - 1Synchros » Exercise - 1 1. The control ........................ synchro has three-phase winding both on its stator and rotor. (a) differential (b) transformer (c) receiver (d) transmitter
    Tags: electrical, engineering
  • Two port network - 2Two Port Network » Exercise - 12. The number of possible combination generated by four variables taken two at a time in a two-port network is : (a) four (b) two (c) six (d) none of these
    Tags: electrical, engineering


Please enter your comment!
Please enter your name here