Dielectrics have the strange property of making space seem bigger or smaller than it looks. The dielectric constant value tells you how much smaller or bigger the space gets. It shows itself in two ways.

First, when you put some dielectric between two electric charges it reduces the force acting between them, just as if you'd moved them apart.

Secondly, the dielectric constant of a material affects how electromagnetic signals (light, radio waves, millimetre-waves, etc.) move through the material. A high value of dielectric constant makes the distance inside the material look bigger. This means that light travels more slowly. It also ‘scrunches up’ the waves to behave as if the signal had a shorter wavelength.

For electromagnetic waves, just like the forces between charges, the dielectric warps the space to make it look a different size.

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