What is that between capacity and ability

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Capacity of a plate capacitor

In the following we consider the already known plate capacitor. This consists of two parallel metal plates that are connected to a voltage source.

The greater the amount of charge that fits on the capacitor at a certain voltage, the greater its capacity. And the lower the voltage that is required to pump a fixed amount of charge onto the capacitor, the greater the capacitance of the capacitor.

The capacitance is therefore a useful quantity to describe the capacity of a capacitor to take up charge independently of the applied voltage. A capacitor can therefore be assigned a capacitance, regardless of whether it is connected to a voltage source or not. Its capacity depends only on the type of capacitor.

We also have the following knowledge about the homogeneous electric field:

  1. The consideration of the voltage in the homogeneous field has shown that, where in the case of the plate capacitor is the distance between the two plates.
  2. A measurement of the force on a test charge or the electric field strength in the homogeneous area between the plates of a plate capacitor shows, where is the area of ​​one plate.

This is easy to understand: the larger the area of ​​the plates on which a certain charge has to be distributed, the lower the field strength between the plates.

Inserting them into one another then results in the capacitance of the plate capacitor

The constant of proportionality also results from measurements to. Here is the known influence constant and the dielectric constant of the medium between the plates. We already know the relative permittivity from the treatment of polarization in dielectric materials.

Capacity of a plate capacitor

The capacitance of the plate capacitor is therefore dependent on its geometry - area and distance between the plates - as well as on the substance that is located between the plates.

With regard to the dimensions, this means: the larger the plates of the capacitor are and the closer they are to each other, the more charge the capacitor can take at a certain applied voltage.

If there is air between the plates of the capacitor, the relative permittivity can be used approximately.

If, for example, a dielectric body is pushed between the plates, the capacitance of the capacitor doubles and it can absorb twice the amount of charge with a constant applied voltage.