Effect of a Dielectric on Capacitance

You must have heard about dielectrics and capacitance. But what effect does a dielectric have on capacitance? Dielectric refers to the ability to induce charges from one another in a substance. A capacitor is constructed with a dielectric material. It has two separate plates, which are parallel. A dielectric in capacitance means an electric insulator can be polarised if an electric field is applied. 

A common example of dielectrics in capacitors is insulating material between capacitors and between its plates. All materials that are dielectrics are also insulators. Capacitors are used to store any electrical energy by having an insulator or nonconducting material, which is called dielectric.  

An electric field is generated when all the charge carriers are removed from the capacitors. This energy is stored via electric fields. 

Dielectrics in capacitors

Dielectrics in capacitors have various uses, effects and applications, as we have seen above. Dielectrics have certain properties and nature that make them suitable for use in capacitors. Many factors such as electric field, charge carriers, permeability, relative permeability, etc, can affect the capacitance of the capacitor in which the dielectric material is introduced. 

The capacitors will have different capacitance if they are partially or filled by the dielectric. Also, different types of dielectric will affect capacitance differently. This is because every dielectric material has different properties. 

The electric field induced by the dielectric material in the capacitor plates, which are parallel, is in the opposite direction of the electric field, which was previously present because of the substance or capacitor.    

Effect of dielectrics on capacitance 

• Dielectrics are bad conductors of electricity; they can store electric charges.
• The energy they emit is generally in the form of heat.
• Dielectrics are placed between two plates of the capacitors, which are parallel so that they can occupy the space between them. 
• The electric field polarises the dielectric in the parallel plates of the capacitor. 
• If the dielectric is added to the capacitor, its density increases compared to the vacuum value.
• The capacitance of the capacitor is directly proportional to the electric field between the parallel plates of the capacitor. 
• The electric field’s strength is reduced when the dielectric is put into it.
• The dielectric ultimately increases the capacitance.

Why are dielectrics used in capacitors?

• Dielectric materials have a very large energy gap between them.
• The dielectric materials have high resistivity.
• Resistance has a negative coefficient of temperature and has high resistance of insulation.
• In dielectrics, the attraction of the nucleus and the electrons is very high and strong.
• In dielectric materials, there is no current because of the absence of free electrons. That is why they have low electrical conductivity. 

Notes on dielectrics and capacitance 

If the dielectric is present in the capacitor, the strength of the electric field is comparatively reduced. The potential difference across the capacitor plates is reduced because the total charge on the parallel plates is kept constant. 

Before the insertion of the dielectric, the capacitance of a material is C= εoA/d. After the dielectric insertion, the material’s capacitance is increased by ‘k’, C= kεoA/d.

Notes for dielectric effect on capacitance 

The capacitance results from the electric flux, which is zero inside the source when the dielectric is introduced in it. This happens as follows: 

The dielectric produces its electric field when it is put into the parallel plates of the capacitor. This is caused due to the polarisation of charges. This electric field is in the opposite direction of the electric field that was initially present in the substance. This results in total zero electric flux. 

If the voltage is kept constant, there will be an increase in the charge of the capacitor. 

The potential in the capacitor will decrease if the capacitor is not connected or the charge is kept constant.

C= εoA/d or C= kεoA/d 

Dielectric in capacitance if the parallel plates are filled with dielectric

If the area between the plates is filled with a dielectric of dielectric constant k, the capacitance will be given by C = k×Co. 

The electric intensity will be reduced by k times.

And then, the capacitance of the capacitor on adding the dielectric will be increased by k times.

Dielectric in capacitance if the parallel plates are partially filled with dielectric 

If the area between the plates is partially filled with a dielectric, then the capacitance becomes C= Aɛo/{d+t(1/k-1)}

Conclusion 

No current flows through dielectrics because they are poor electric current and electric charge conductors. Dielectrics have no use in conductors. The atoms of dielectric material are not ionised, rather they are polarised. 

For instance, if you bring any negatively charged object near the dielectric, its electrons will be repelled, which means that a positively charged side is facing the negatively charged object. 

A condition for a dielectric to be a good dielectric material is that it should not only be an insulator but should also not get ionised in any situation. A better dielectric material can be one that can perform in high temperatures for capacitors. 

Capacitors with dielectric materials in them have a wide range of uses in industry and chemistry.