this post was submitted on 20 Jan 2025
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The electric field one is also interesting, because the cable length doesn’t actually determine how long it takes to turn on. All that matters is the distance between the power source and the device. Electricity travels at the speed of light, which means we can measure how long it should take to travel down the wire.
But let’s say you have a 1 light year long power cable, made out of a perfect conductor (so we don’t need to worry about power loss from things like wire resistance or heat). Then you set the power source right next to the device and turn it on. The logical person may say that the device would take a full year to turn on, because the cable is one light year long. Others may say that it will take two light years to turn on; Long enough for the electricity to make a full circuit down the cable and back to the power source again.
But instead, the device turns on (nearly) instantly. Because the wire isn’t actually what causes the device to turn on. The device turns on because of an EM field between itself and the power source. The wire is simply facilitating the creation of that field. The only thing that matters is the distance between the source of power and the device. That distance, divided by the speed of light, is how long the device will take to turn on. If the device was a full light year away from the power source, it would take a full year to turn on. But since the device is sitting right next to the power source, it turns on right away.
wait so if you have another person travel to the other end of the wire, and do a time sync with consideration of time dilation to tell them to cut the wire 1hr after you turn on the power, will the device turn off after 1 year since it wouldn't "know" the wire is cut until a year has passed?
Can you help me understand why the distance between the power source and the load impacts how long it would take to turn on? I remember a video a while back (veritasium maybe?) that explained it like metaphorically pushing/pulling a chain inside the wire, but why would distance to the source impact this?