Question

What is K in capacitance?

Answer 1

Capacitance is the ability of a material to store charge inside it. The capacitance of capacitors depend on the physical dimensions like area of cross section, length etc. It also depends on the medium inside the capacitor. The medium can be air, vacuum or dielectric can also be introduced between the capacitors.

Complete answer:
Capacitance is the ability of a material to store charge inside it. Its SI unit is Farad (F). The capacitance for a parallel plate capacitor is-
$C=\dfrac{K{{\varepsilon }_{0}}A}{d}$ - (1)
Here, $C$ is the capacitance
${{\varepsilon }_{0}}$ is the permeability of free space
$A$ is the area of cross section
$d$ is the distance between the plates
$K$ is the dielectric constant
The dielectric constant of air is 1. A dielectric is an insulating material introduced between capacitors. When the dielectrics are introduced between a capacitor, polarization occurs within it due to which an electric field is produced which is opposite to the field inside the capacitor.
From eq (1),
$C\propto K$
Therefore, the capacitance of a capacitor is directly proportional to the dielectric constant. It also affects the potential difference, charge stored and energy of the capacitor.
Therefore, the $K$ in capacitance stands for the dielectric constant.

Note:
Polarization occurs because the electrons in the dielectric cannot flow as it is an insulator. The dielectric decreases the net electric field inside the capacitance and hence capacitance increases and so charge also increases but the potential difference across the capacitor decreases. Whether the energy increases or decreases depends on the parameters which will be constant. The dielectrics can be inserted as a series or parallel combination too.