Directional wires/cables

@jea48

I think the answer is instantly. The switch is opened, Games over.

This was in response to what happens when a light is switched off, and of course the answer given is so wrong on so many levels!

When the light is on, it is because power is delivered in an electrical circuit featured by voltage and current - likely to be direct current in a car or alternating current in a home. When the current is suddenly interrupted because the switch is thrown, electrical pressure builds up at the switch. This pressure is known as voltage. If the current was big enough, the voltage becomes high enough to ionise the surrounding air and cause sparks at the switch contacts.

This is precisely the phenomenon used by older car ignition systems to generate very high voltages from 12-Volt DC electrical systems.

On another level, the light will keep generating light as the current it receives slowly dies away. High power incandescent lamps will still be hot enough to shine for a while after receiving no power at all.

Albert Einstein would assert that nothing can travel faster than the speed of light in a vacuum. It would take at least that long for the signal from the switch to reach the bulb. He would also say that there is no such thing as a single instant. Time is relative to where you are and how fast you are moving. Your ’instant’ is different to mine! But you claim to know all this stuff?

@rodman99999 

Were it the DC voltage/current, from an amp's power supply, modulated by the amp's output devices, into an amplified musical signal; it would appear much more complex, but: still a sinusoidal wave

The musical signal is more than a sinusoidal wave, otherwise it would not be considered musical!  We talk of the harmonics that make say a flute sound like a flute, or an electric guitar sound like the distorting amplifier it is connect to.

Fourier theory has it that any repeating waveform or musical note can be represented as an infinite sum of sinusoidal waves, being the base frequency plus all the possible harmonics or overtones.  You can create a graph of the frequency spectrum of the note, although the original note exists entirely in the time domain.

You can apply a mathematical Fourier transform to convert the time domain into the frequency domain, and back again (but not perfectly).

This idea is so pervasive that many audiophiles speak and think in the frequency domain - the treble does this, the midrange does that, and the bass something else.

The only thing I can think of in nature that converts the time domain to the frequency domain is our ear / brain system, which fires complex patterns of neuron activity where the original neurons which fire respond to particular frequencies, but fire at rates depending on loudness.  The initial firing pattern depends on arrival patterns in time.

There are a couple of issues.  Obviously we do not hear high frequency harmonics above say 20-kHz.  To reconstruct sharp transients (for example square waves) very high frequency harmonics are needed to capture the leading edge.  And mathematically without these high frequencies the Fourier transform wobbles before and after the leading edge.  As more higher frequencies are added, a spike appears extending the leading edge.  Ouch

      For anyone interested in expanding their understanding of sinusoidal/audio signals, without a lot of semantic gymnastics:

              https://www.allaboutcircuits.com/video-tutorials/applications-of-sinusoidal-signals/

Albert Einstein would assert that nothing can travel faster than the speed of light in a vacuum.

        And: proven wrong, by some of the most vigorous testing/experimentation in Physics, as mentioned previously and (obviously) ignored by the Dunning-Kruger sufferer above.

                                                     ie:

   https://www.caltech.edu/about/news/proving-that-quantum-entanglement-is-real

           The willful ignorance on this site has become SO very tedious.

                           QED (repeatedly)?

                          Mostly: non sequitur!