What is the adjusted speed of electromagnetic energy in coax or antenna wire?

What is the adjusted speed of electromagnetic energy in coax or antenna wire?

• A. 285,000,000 meters per second.
• B. 299,792,458 meters per second.
• C. 180,000,000 meters per second.
• D. 1,000,000,000 meters per second.

Answer: (A)

The signal speed in coax or a wire is the propagation speed of the electromagnetic wave along the line. This speed is nearly the speed of light in vacuum but reduced by the dielectric material surrounding the conductors. The speed of light in vacuum is about 299,792,458 m/s. In coax, the wave travels through the dielectric, so its velocity is this vacuum speed multiplied by the velocity factor (a number less than 1 that depends on the dielectric). For many coax cables, the velocity factor can be around 0.95, giving roughly 0.95 × 299,792,458 ≈ 285,000,000 m/s. That’s why the adjusted speed is about 285 million meters per second. The other options would imply either the full vacuum speed (not applicable inside the cable), a significantly slower speed that would correspond to a much denser dielectric, or a speed faster than light (which isn’t possible in ordinary media).

The signal speed in coax or a wire is the propagation speed of the electromagnetic wave along the line. This speed is nearly the speed of light in vacuum but reduced by the dielectric material surrounding the conductors. The speed of light in vacuum is about 299,792,458 m/s. In coax, the wave travels through the dielectric, so its velocity is this vacuum speed multiplied by the velocity factor (a number less than 1 that depends on the dielectric). For many coax cables, the velocity factor can be around 0.95, giving roughly 0.95 × 299,792,458 ≈ 285,000,000 m/s. That’s why the adjusted speed is about 285 million meters per second.

The other options would imply either the full vacuum speed (not applicable inside the cable), a significantly slower speed that would correspond to a much denser dielectric, or a speed faster than light (which isn’t possible in ordinary media).