Final answer:
The statement is true; the dielectric constant measures the ability of a material to act as a dielectric and is defined as the ratio of electric fields in a vacuum to that in the dielectric material.
Step-by-step explanation:
The statement is true: a material's dielectric constant rates how well the material acts as a dielectric compared to a vacuum. The dielectric constant of a material is denoted by k (sometimes written as ε_r) and is defined as the ratio of the electric field in a vacuum (Eo) to that in the dielectric material (E). This constant is a measure of a material's ability to reduce the electric field within it and is directly related to the polarizability of the material.
When a dielectric material is inserted into a capacitor, it increases the capacitor's overall capacitance by reducing the net electric field between the plates, leading to a capacitance given by C = ε_rε_o A/d (where ε_o is the permittivity of free space, A is the area of the capacitor plates, and d is the separation between them). This increase in capacitance allows capacitors to store more charge for a given voltage. For air or vacuum, which has a dielectric constant very close to 1, the capacitance remains nearly unaffected; this underlines that a vacuum is considered the baseline for dielectric properties.