Question

what is the value of dielectric constant of a metal?​

Answer 1

Metal's dielectric constant depends on external electromagnetic field. For a low frequency field, metal's dielectric constant is a complex, with a very high imaginary part. As the field frequency increases, its dielectric constant can become a negative value, meaning metal reflects the electromagnetic wave in this frequency domain. When the frequency becomes even higher, metal's dielectric constant becomes a positive value, meaning metal acts as a "normal" dielectric medium.