 # Electrostatic Potential and Capacitance

## Electric Potential at a point is the work done per unit charge in bringing a charge from infinity to that point. Electric potential is the scalar quantity and its unit is volt (V). Mathematically, it can also be represented as the ratio of charge to position vector from the origin. Potential due to a dipole depends not just on r but also on the angle between the position vectors. Equipotential surfaces are the surfaces which have same electric potential at every point on the surface. Electric potential decreases with the increase in the distance from the charge. Electric field is in a direction in which potential decreases fastest. The magnitude of electric field at a point is change in magnitude of potential per unit displacement normal to the equipotential surface at that point.      Due to electric potential, the charges possess a potential energy. The potential energy of the system of two charges is the total work done in assembling the configuration. The substances having mobile charge carriers are known as Conductors. Dielectrics are insulators which do not allow the electric current to pass through it. However, when an external field applied, induced charges are produced on them. These materials do not have mobile charge carriers and hence the induced electric field in them doesn’t cancel out the external field. A device that is used to store electrical energy is known as Capacitor. Capacitors can be classified as parallel plate capacitor, spherical capacitor or cylindrical capacitor. Capacitance of a capacitor is the ratio of charge to the potential difference. It depends on the geometrical shape of the plates and the medium between the plates. The medium between plates is generally dielectric. When two large plane conducting plates are separated by a small distance then it will form a parallel plate capacitor. A parallel plate is an arrangement which can be charged to large extent in a small area. A dielectric medium of dielectric constant K when placed between the plates of a parallel plate capacitor, the capacitance of the capacitor increases K times. Just like resistors, capacitors can be connected in series and parallel. In series combination, capacitors are connected end to end. The equivalent capacitance in this case is always less than the individual capacitance. In parallel combination, capacitors are connected such that their plates are connected to a common point. The equivalent capacitance in case capacitors joined parallel, is always greater than the individual capacitance. To charge a capacitor, a work has to be done to transfer the charge from plate at lower potential to the plate at higher potential. This work gets stored as the potential energy of the capacitor.

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