KCET Electrostatic Potential and Capacitance Topics 2025

KCET Electrostatic Potential and Capacitance Topics 2025: Electrostatic Potential and Capacitance constitute an important section of the KCET Second-Year PUC Physics Syllabus. Candidates looking for admission through the KCET 2025 exam must know the list of important topics under the Electrostatic Potential and Capacitance section. Electric Potential Energy, Capacitors and Capacitance, Electrostatics of Conductors, The Parallel Plate Capacitor, Combination of Capacitors, Dielectrics, and Polarization are some of the KCET Electrostatic Potential and Capacitance topics. Preparing such topics in the required manner is an excellent approach which will help the candidates gain an advantage in the KCET 2025 exam . We have noted down all the key topics of Electrostatic Potential and Capacitance from the KCET 2025 syllabus. Candidates are advised to read the article thoroughly for detailed information related to the KCET Electrostatic Potential and Capacitance Topics 2025.

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KCET Electrostatic Potential and Capacitance Topics 2025

Electric Potential Energy

When one moves around in the gravitational field of the earth, one needs to make efforts. Simply stating, one has to work by exerting force if one wants to change one position in a field. Electric charges have fields around them and hence a charge has to do work if it intends to change its position. This work refers to the electric energy or the electric potential energy of the charge.

It is a known fact that central forces are conservative in nature which implies that the work done on any particle moving under its influence does not depend on the path taken by the particle but depends on the initial and final positions of the particle. For the conservative forces, work done on particles undergoing displacement can be expressed in terms of the potential energy function.

Capacitors and Capacitance

What is a Capacitor?

Capacitors are also known as electric-condensers which are two-terminal electric components. Capacitors have the ability or capacity to store energy in the form of electric charge and they are designed to enhance and increase the effect of capacitance. Hence, capacitors take into account properties such as size and shape. The storage capacity of capacitance ranges from small storage to high storage.

Capacitance

Capacitance refers to the ability of a capacitor to store energy in the form of electric charge. In simple words, the capacitance is the storing ability of a capacitor which is measured in farads.

Construction of Capacitor

Most capacitors usually comprise two electrical conductors. Sch conductors are separated by metallic plates. Conductors may be in the form of electrolytes, thin film, a sintered bead of metal etc.

Capacitor Rating

The capacitance value of two different capacitors may exactly be the same and the voltage ratings of the two capacitors are different. Taking into consideration two capacitors, one which has a small voltage rating and the other with a high voltage rating, one can substitute a smaller rated voltage capacitor in place of a higher-rated voltage capacitor. This can occur as the result of unexpected increases in voltage. The common working DC voltage of capacitors are usually 10V, 16V, 25V, 35V, 50V, 63V, 100V, 160V, 250V, 400V and 1000V.

Electrostatics of Conductors

Electrostatic Properties of Conductors

Conductors contain mobile charge carriers. In metallic conductors, these charge carriers are electrons. In a metal, the outer electrons separate from their atoms and are free to move. These electrons are free to move within the metal but not free to leave the metal. When an external electric field is applied, it migrates in the opposite direction of the field. The positive ions consist of the nuclei and the bound electrons, which remain fixed in their positions. In electrolytic conductors, both positive and negative ions act as charge carriers. Here are some important points about the electrostatic properties of a conductor:

I. The electrostatic field remains void within a conductor

In the static condition, whether a conductor is neutral or charged, the electric field inside the conductor is zero everywhere which is one of the defining properties of a conductor. A conductor contains free electrons that experience a drift or a force in the presence of an electric field. Inside the conductor, the electrons distribute themselves in such a manner that the final electric field at all points inside the conductor is zero.

II. Electrostatic field lines are normal to the surface at every point in a charged conductor

If the electric field lines were not perpendicular to the surface, there would be a component of the electric field parallel to the surface of a conductor in the static condition.. Hence, free charges moving on the surface would also have experienced some force leading to their motion. But, this does not happen. Since there are no tangential components, the forces must be perpendicular to the surface.

III. In the static conditions, the interior of the conductor contains no excess charge

Any neutral conductor contains an equal amount of positive and negative charges, at every point which holds true even in an infinitesimally small element of volume or surface area. From Gauss’s law, it can be said that in the case of a charged conductor, the excess charges are present only on the surface.

IV. Consistent electrostatic potential within the volume of the conductor

The electrostatic potential at any point throughout the volume of the conductor is always constant and the value of the electrostatic potential at the surface is equal to that at any point inside the volume.

The Parallel Plate Capacitor

Parallel Plate Capacitors refer to the type of capacitors which comprise of an arrangement of electrodes and insulating substance which is (dielectric). The two conducting plates act as electrodes and there is a dielectric between them which acts as a separator for the plates. The two plates of the parallel plate capacitor are of equal dimensions and are connected to the power supply. The plate, connected to the positive terminal of the battery, acquires a positive charge whereas the plate connected to the negative terminal of the battery acquires a negative charge. Due to the attraction, charges are in a way trapped within the plates of the capacitor.

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The Principle of Parallel Plate Capacitor

It is known that one can give a certain amount of charge to a plate. If more charge is supplied to a plate, its potential increases and it can lead to a leakage in the charge. If another plate is placed next to the positively charged plate, then the negative charge flows towards the side of the plate which is closer to the positively charged plate.

As both the plates have charges, the negative charge on plate 2 will reduce the potential difference on plate 1 whereas the positive charge on plate 2 will increase the potential difference on plate 1. However, the negative charge on plate 2 will exert a higher impact. Hence, more charge can be given on plate 1. Because of the negative charges on plate 2, the potential difference will be less. This is the principle of the parallel plate capacitor.

Energy Stored in a Capacitor

Action has to be commenced in order to transfer charges upon a conductor, against the force of resistance from the already existing charges on it. This work is stored as a potential energy of the electric field of the conductor.

It is taken into consideration that a conductor of capacity C is at a potential V0 and q0 is the charge on the conductor at this instant. The potential of the conductor when (during charging) the charge on it was q (< q0) is,

V ∝ q or V = Cq; where ‘C’ is a constant of proportionality which depends on the nature of the material of the conductor. This constant is known as the capacitance.

If one wishes to transfer more charge to this conductor, work has to be done against the repulsive forces of the charges already present on the conductor. If one has to transfer a small charge ‘dq’ which takes a small amount of work ‘dW’, then work done in bringing a small charge dq at this potential (V) is =

Combination of Capacitors

What are Conductors and Insulators?

Conductors refer to such materials via which electric charge can pass easily. Whereas, electric charges can’t pass easily through insulators. Such is the key difference between the two.

Capacitors

The potential V of a conductor is dependent upon the charge Q provided to it. According to the observations, the potential of a conductor is proportional to the charge on it.

Q ∝V or Q = CV

The proportionality constant ‘C’ is known as the capacitance of the conductor. Hence,

C = Q/V

The capacity of a conductor refers to the ratio between the charge of the conductor to its potential. If V = 1, then C = Q. The capacity of a conductor is the charge required to raise it through a unit potential.

Units

• S.I Unit: Farad (coulomb/volt). The capacity of a conductor is said to be 1 farad if a charge of 1 coulomb is required, to raise its potential through 1 volt.
• C.G.S – stat farad (stat-coulomb/stat-volt). The capacity of a conductor is said to be 1 stat farad is a charge of 1 statcoulomb is required, to raise its potential through 1 statvolt.

Dimension of C:- [M-1L-2T4A2]

Dielectrics and Polarization

What is a Dielectric?

Dielectrics are non-conducting substances which are insulating materials and are bad conductors of electric current. Dielectric substances can hold an electrostatic charge along with passing minimal energy in the form of heat. Some examples of dielectric are Plastics, Mica, Glass, Porcelain and various metal oxides. One must keep in mind that even dry air is also an example of a dielectric.

Classification of Dielectrics

Dielectrics are of  mainly two types:

1. Polar Molecules: They refer to those types of dielectric where the possibilities of the positive and negative molecules coinciding with each other are null or zero. This is so as they all are asymmetric in their shapes. Some examples of polar molecules are H2O, CO2, NO2 etc. When the electric field is not present, it causes the electric dipole moment of these molecules in a random direction making the average dipole moment zero. In case the external electric field is present, the molecules arrange themselves in the same direction as the electric field.

Van De Graaff Generator

A Van de Graaff generator is an electrostatic generator invented by American physicist, Robert J. Van de Graaff. It makes use of a moving belt which accumulates charge on a hollow metal structure. The generator has a design of a globe, placed on the top of a column which is insulating in nature.

The generator creates a very high electric potential in the order of a few million volts which results in a very large electric field. This electric field is used to accelerate charged particles.

Working Principle of The Generator

A large spherical shell of radius R can be taken into consideration. If one places a charge of magnitude Q on such a sphere, the charge will spread uniformly over the surface of the sphere. The electrical field within the sphere is zero, and the one outside the sphere is because of the charge Q at the centre of the sphere. Hence, the potential outside is that of a point charge; and inside it is constant. We, thus, have:
Potential within conducting spherical shell of radius R comprising charge Q = constant and is as follows

Let us place a small sphere at the centre of the large one in a way that the radius of the smaller sphere is r and the charge upon its surface is called q. Upon the surface of the small sphere:

At the large spherical shell of radius R:

If we take into consideration the total charges in the system, i.e, q and Q, then the total potential energy because of the system of charges is:

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