Physics notes on Parallel plate capacitor with dielectrics

A Parallel plate capacitor refers to a type of capacitor that arranges a capacitor using electrodes and insulating material or dielectrics. Two parallel plate capacitors act as electrodes. A dielectric is always present between them, which acts as the separator for the plates. Two plates of the parallel capacitor are always of the same dimension. Each plate is connected to the power supply. 

These capacitors are mainly used in batteries or rechargeable energy systems. This capacitor is also used in dynamic digital memory systems. In pulses, lasers and radars, the use of this capacitor is also significant. This chapter of parallel plate capacitors will cover the detailed understanding of each capacitor, the formula of calculating the capacitor energy, its basic principle and the relation of the capacitor with dielectrics. 

Concept of Parallel plate capacitor 

In a parallel plate capacitor, two metallic plates are placed facing each other and separated by a dielectric material. The dielectric medium can be a vacuum, air or some non-conducting material like wool, paper, glass, mica, electrolyte gel, etc. The dielectric property prevents the current flow through the plate due to the non-conductive property. 

The dielectric material makes the atoms polarised under the effect of the electric field. The voltage source forms the polarisation, due to which positive and negative charges get deposited in the parallel plate capacitor. When we connect the DC source with the capacitor, it behaves like an open circuit across it. On the other hand, it acts as a short circuit when connecting it with the AC source. The prosperity of parallel capacitors makes a suitable place for filtering harmonics from the AC supply. It is also used for tuning purposes in the electric circuit for different applications. 

This capacitor also can act as a transducer application. Along with that, it also can be used as a source of capacitive reactive power. It can serve as an important element in supplying power system auxiliaries for improving the system’s power factor. In addition, it enhances the stability of the system. A Parallel plate capacitor can also be used as an energy storage device. 

Concept of dielectric

A dielectric is a kind of insulator that shows polarisation properties in the presence of an electric field. These materials are poor conductors of electricity since they do not possess free electrons like normal electrical conductors. However, in the presence of an electric current, the equilibrium of the electrons slightly shifts in the opposite direction. It is because the positive charges get aligned to the direction of the applied field. This phenomenon is known as dielectric polarisation.

Due to dielectric polarisation, an internal electric field gets generated that lowers the impact of the outside field on the dielectric. In other words, the charged particles inside get polarised and align themselves in or against the direction of the field. When the field is removed, the particles return to their earlier equilibrium state. Dielectric materials store and dissipate energy. One of the main applications of dielectric mediums is in a parallel plate capacitor.

Details of Parallel plate capacitor formula

The formula of The Parallel plate capacitor can be denoted by, 

C=Kϵ0(A/d)

Here, K is related to the relative permittivity of dielectric material. D is the distance between the two plates, A is the area of the plates and ϵ0 is the space of permittivity. 

Principle of Parallel plate capacitor 

We know we can provide a certain amount of charge to a plate. But if we charge more on a plate, then the potential increases and causes leakage in the charge. If we put another plate next to the positively charged plate, then the negative charge will flow towards the side of the plate, which is closer to the positively charged plate. 

When both the plates are charged, the plate with a negative charge will reduce the potential difference on plate 1. But the negative charge on the second plate will have more impact so that more charge is transferred to plate 1. Therefore, the potential differences will be less due to the negative charge on plate 2. It is the principle behind a parallel plate capacitor. 

Conclusion

We can’t use this capacitor as the storage of energy because the energy storing capacity of the magnetic field is higher than the capacity of the electric field. The dielectric also has some disadvantages. Due to leakage of charge, it cannot hold a charge for a long time and therefore we cannot use it as the ideal charge stirring device. 

This chapter has covered all the aspects related to parallel plate capacitors and the importance of dielectrics in stirring energy and controlling energy flow. Along with that, it is discussed about the formula of calculation, to make it more clear and understandable.