Question

Is the speed of electricity =the speed of light?

Answer 1

The speed of electricity is conceptually the speed of the electromagnetic signal in the wire, which is somewhat similar to the concept of the speed of light in a transparent medium. So it is normally lower, but not too much lower than the sped of light in the vacuum. The speed also depends on the cable construction. The cable geometry and the insulation both reduce the speed. Good cables achieve 80% of the speed of light; excellent cables achieve 90%. The speed does not directly depend on the voltage or resistance. However, different frequencies have different attenuation. In your example, the very moment of switching on represents a high frequency front that will be attenuated. While at the input the voltage would increase very fast, at the output it would increase gradually, as if with a delay. It is not really a delay per se, because the initial low level signal would get there almost with the speed of light, but its amplitude would only gradually increase and reach the full voltage with a substantial delay that would depend on the cable and circuit impedance (mostly on the cable inductance). If you use a high speed coaxial cable (like a 3GHz satellite TV cable) instead of a wire, the delay would be much shorter (80-90% of the speed of light to the full voltage). Hope this helps.