Is there a way to prevent electricity flow without physical intervention

Question

Is there a way to put an external switch on a lightbulb cable, in order to create an external switch to prevent and allow electricity flow?

Without using any massive electromagnets or the likes...

Answer 1

It's a interesting question if I understand its meaning. I think you should define what you mean by "physical intervention" however. In order to answer I'll assume you mean to ask the following:

"Assume a double wire is connected to an AC outlet, and electric current is flowing due to the voltage drop across the resistance of both the wire and the bulb. Is there a way to prevent electricity flow in the wire without changing the properties of the wire, disrupting the wire, connecting other wire or wires directly or obstructing the wire?"

ASSUME WE ARE NOT TALKING ABOUT DC CURRENT!

The answer is YES, but you need to separate the wires leading to/from the outlet and add a device. Below I describe a device (two actually) inserted between the wires. Note that if you plan to do this yourself it is possibly quite dangerous! But you didn't ask about the danger, so we'll approach this theoretically in your case and add some warnings (and fuses:-)

The wonderful thing about AC is that the current is always changing. It moves in one direction, varies its strength in that direction, and then reverses so that it moves in the opposite direction with its strength now varying in that direction. This dance repeats as long as the bulb is on (in your case). This continual variation means there is always a small voltage drop induced across the wire in the OPPOSITE direction of the current (well ... sort of opposite - more on that below), because that's what happens when currents change strength and direction: the magnetic field surrounding the wire changes and a changing magnetic field creates an electric field which somewhat opposes the electric field which created the magnetic field. And on and on it goes. This induced electric field is small in the case of AC, because for almost all cases the current is changing very slowly (60 hz is a low frequency and results in a very small voltage drop due to a very small induced electric field.)

When you pull the two wires apart you increase the amount of magnetic field that is in between the wires. The more magnetic field between the wires the greater the change of that magnetic field in between the wires (remember the AC current is always changing!) and the larger the voltage drop induced in the (somewhat) opposite direction within the wires. What you want to do now is insert a device in between the wires that will change the phase of and amplify this magnetic field in between the wires. How to do that???

Here's one way. Separate the double wire in TWO places as far apart as possible. Take a long thick wire (at least 16 gauge) and tape it along the space inside of one of the open areas you created when you separated the wires. Now loop it around again and again. For instructional purposes I'll say loop it around 10 times - the more the better but eventually you get something too big and heavy. The more area inside this loop the better, so you'll need to decide how much to separate the wires. Left alone this new wire loop will also have an electric field induced within it, and always in the same direction as the electric field induced in the bulb wire.

Now do the same thing again with another wire. You now have two loops of wire, again as far apart as you can get them. The farther apart they are the less the magnetic field from one loop affects that of the other.

The wire loops now have a very tiny AC voltage across their leads. One that somewhat opposes the current in the bulb wire. We want to take that small loop voltage and amplify it in the OTHER loop so that we now have a large current just correctly out of phase so that it induces a voltage drop exactly opposite to that of the bulb wire current! This is where things can get dangerous, because the amplification can be very large if we allow it to be. So instead of amplifying that loop current immediately, we change the amplification slowly meaning your bulb will turn off over time rather than immediately. How much time? You decide. I'll aim for 2 seconds, but the real value comes down to the specific implementation.

At this point you'll need an electrical engineer to help with the amplifier. Since some op-amps can handle large currents the most simple circuit I can think of (any EEs out there know something simpler here?) would be with a high current op-amp or op-amps in parallel, a couple of resistors and some VERY well chosen capacitors to prevent some crazy oscillations (or not if you want to strobe and blow fuses;-). Again, an EE or very careful EE wannabe needs to build this and there needs to be a fuse inline! Now take the leads from your first looped wire, connect it to your amplifier inputs, take the leads from the other looped wire, connect those to the amp output (be careful to connect the leads correctly and not in reverse) and turn the amplifier on. If your amplification is high enough the bulb will turn off, but do it this way and you've got a VERY DANGEROUS device in your house because the amount of current flowing in that loop is enormous. Without the inline fuse the op-amp will overheat and most likely your fuse box (breaker switches) will fry or flip! Fortunately we can do two things to keep this from happening ...

1. Add some iron inside the loops - this will allow you to use a lower current amp. You can't use any iron, but iron you know that magnets will attract to. You said you don't want "heavy" so maybe no iron, but if you can find some that's not too heavy you can also tape it inside the loops. TAPE IT FIRMLY AND ENSURE THAT IT COVERS AS MUCH OF THE LOOP AREA AS POSSIBLE. You don't need to add iron - not needed but it will cut down on the amount of current needed by your amp. Sorry, but I don't know where to find iron for this purpose. Google it or just sift a lot of it out of sand and glue it together in the right shape. Just a random suggestion there, but hey if you've got a lot of iron in your sand ... juss sayin.

2. Add a high resistance potentiometer (a.k.a the "pot") to your amplifier circuit. Your EE will need to choose the pot. Turn the pot all the way up (highest resistance) so that there is no (or almost no) amplification from the amplifier. Now when you turn on the amplifier nothing will happen - the bulb will stay on. SLOWLY turn the pot until the bulb starts to dim. Continue turning SLOWLY until the bulb is off. STOP. Don't let the pot turn any more than this. Now turn OFF the amplifier.

That's almost it. What you do now is turn on the amp and see how long the bulb takes to turn off. Adjust the pot SLOWLY. Turn amp off then on. Continue SLOWLY turning the pot until you get to your 2 second turn off or whatever you've chosen.

OK! Yeah it's dangerous, but so is everything in your house and car that uses electricity until it's built correctly. SO BUILD IT CORRECTLY AND IT WILL BE A VERY COOL DEVICE! Why do I think it's cool? Because once the bulb is off there is no longer much current in the bulb wire (there will be some however - this is NOT as efficient as an inline switch). Less current means less induced electric field which means less current amplification by the amplifier "switch". No, I cannot promise that the bulb will turn all the way off - you need to build and test, but I'm almost certain your results will be best with LED lighting.

Note, the less current needed by the bulb the better and less dangerous this device will be until you get it right. All the better reason to use a low power compact fluorescent or LED bulb.

DISCLAIMER: If current requirements are too large the above instructions will only result in blown fuses. VERY WISE to start this project using a very low power LED bulb. Maybe something like 5 Watts.