As a conductor’s diameter increases, what is the effect on its electrical length?

Electrical length is a measure of a conductor's length expressed in terms of the wavelength of a signal traveling through it. Because electromagnetic waves travel slightly slower along a bare wire than they do in a pure vacuum, a wire's electrical length is longer than its physical length would suggest in free space. As the diameter, or thickness, of an antenna or conductor increases, the capacitance per unit length between the conductor and its surroundings also increases. This extra capacitance lowers the velocity factor, slowing down the phase velocity of the wave traveling along the conductor even further. Because the wave travels slower, a given physical length of thick wire will contain a larger fraction of a wavelength compared to a thin wire. Therefore, increasing the conductor's diameter increases its electrical length, meaning you must physically cut a thick antenna shorter than a thin one to achieve the same resonant frequency.