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A capacitor is a device that stores electrical energy. It consists of two conductors in close proximity. Both conductors are isolated from each other. The simplest example that can be provided here is the parallel plate capacitor. A capacitor has many vital applications. It is used in digital circuits to prevent the loss of information stored in large computer memories. In case of temporary power loss, these capacitors maintain the information. Capacitors are also used as filters to divert spurious electric signals, preventing damage caused by an electric surge.
What is a Dielectric?
A dielectric is an insulating material. Alternatively, it can be defined as a very poor conductor of an electric current. When placed in electric fields, almost no current flows in them. The reason is that they don’t have any loosely bound or free electrons that can drift through the material. Electric polarisation is what occurs here.
Electric polarisation denotes the positive charges within the dielectric getting displaced minutely in the electric field’s direction. The negative charges get displaced minutely in the opposite direction of the electric field.
Role of Dielectric in a Capacitor
A dielectric performs three main functions in a capacitor:
It prevents the conducting plates from coming in contact. This allows for a smaller plate separation, which results in higher capacitances.
It reduces the electric field strength, resulting in an increase in the effective capacitance. This means we get the same charge but at a lower voltage.
It also reduces the possibility of shorting out due to sparking during its operation at a high voltage. The formal term for sparking is dielectric breakdown.
Capacitor With Dielectric Medium
A dielectric layer is placed between two parallel charged metal plates. In this case, the electric field should point from right to left. The positive nuclei of the dielectric will then move with the field to the right. The negative electrons move against the field to the left. Since field lines start on positive charges and end on negative charges, the electric field within each stressed atom of the dielectric will point from left to right. This will be opposite the external field of the two metal plates. Here, the electric field is a vector quantity. And when two vectors point in opposite directions, to get the resultant, you subtract their magnitudes. The overall result will be a weaker electric field between the two plates as the two fields don’t cancel in a dielectric as they would in metal.
Parallel Plate Capacitor
A parallel plate capacitor has electrodes and insulating material arranged in parallel patterns. The two conducting plates are the electrodes. The dielectric is placed between them. This serves as a divider for the plates. The capacitor’s two plates are of similar sizes. The plates get plugged into the power source. Linked to the battery’s positive terminal, the plate receives a positive charge. The plate, which is linked to the negative terminal of the battery, receives a negative charge. The charges get trapped inside the capacitor plates as a result of this attraction.
Capacitance
The amounts of charge for the same applied voltage differ in different capacitors. Their capacitance C is defined to be such that the charge Q stored in a capacitor is proportional to C. The charge stored in a capacitor is given by Q=CV.
Rearranging the equation, it is obvious that the capacitance C is the amount of charge stored per volt or C = QV.
Farad or F is the unit for capacitance and was named for Michael Faraday.The capacitance of a parallel plate capacitor without a dielectric medium is given as C=ϵ₀Ad .
How Dielectric Increases Capacitance
Dielectric increases capacitance due to the polarisation of the insulator. The more the ease of polarisation, the greater will be its dielectric constant, K. For example, water. Water is a polar molecule because one end of the molecule possesses a slightly positive charge and the other end has a slightly negative charge. Water’s polarity causes it to have a relatively large dielectric constant of 80.
The formula for the capacitance of parallel plate capacitor with the dielectric medium is
C= κϵ₀Ad
Where k denotes the dielectric constant of the material.
Conclusion
Capacitors are devices used to store electric charges. Capacitors composed of two identical, parallel conducting plates separated by a distance are called parallel plate capacitors. Capacitors make use of dielectric to insulate the two metal plates of the capacitor. The use of dielectric increases the capacitance of the capacitor and makes it more effective. Parallel plate capacitors have electrodes and insulating material that is arranged in parallel patterns, and the dielectric is placed between them. Although an ideal capacitor does not need any dielectric, it would need to have a vacuum between the plates. But since it is difficult to fit capacitors with vacuum in the modern-day, dielectrics are used in between the plates. The capacitance of a parallel plate capacitor without a dielectric medium is lesser than the capacitance of a parallel plate capacitor with a dielectric medium.
