The velocity factor of a transmission line depends mainly on which property?

Introduction / Context:
The velocity factor of a transmission line represents the ratio of signal propagation speed along the line to the speed of light in vacuum. It is critical for timing, phase delay, and wavelength calculations in RF and communication systems.

Given Data / Assumptions:

• Transmission line filled with dielectric material.
• Velocity factor (VF) = v / c.
• v = velocity of wave in line, c = velocity of light in vacuum.

Concept / Approach:

The propagation speed in a line depends on the dielectric constant (relative permittivity) of the insulation material. Higher permittivity slows down the wave, reducing velocity factor. Temperature and skin effect mainly affect losses, not VF.

Step-by-Step Solution:

Verification / Alternative check:

Cables with polyethylene dielectric (εr ≈ 2.25) have VF ≈ 0.67. Teflon (εr ≈ 2.1) → VF ≈ 0.69. These match practical data.

Why Other Options Are Wrong:

• Temperature: affects loss, not speed directly.
• Skin effect: influences attenuation at high frequencies.
• None of the above: incorrect as permittivity is main factor.
• Magnetic permeability: usually close to 1 in dielectrics.

Common Pitfalls:

Confusing VF with attenuation factor; assuming conductor properties dominate propagation velocity.

Final Answer:

Relative permittivity of dielectric material