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What makes an ac voltage detector work?

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Quetzalcoatul

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Im trying to find out which makes a/ ac voltage detecto work, capacitors, voltage amlifier, magnitude sensor, or op amp? Im trying to help with a youngsters science project
 
There are AC voltage and AC current detectors.

Voltage could be very simple. If you ever places your hand on a scope probe, you would see your body pick up a huge 60 cycle signal.
So, I would image that a high Z amp connected to an antenna (piece of wire). You might need a 10 M to ground. The output of the OP amp could drive an LED. This is an electric field. I would image that there might be some frequency selection applied to the output.

Current is an Electro Magnetic Field. Not sure how this might work. It may work on (Google hall effect current sensor") principle or it may use a small transformer or ferrite antenna.
 
Hi Quetzalcoatul. Welcome to ETO! :)

The simplest AC detector has a probe connected to an op-amp, and the output is connected to a headphone jack. If the probe comes near AC, the electro-magnetic field given off by the AC conductor induces current in the probe. The op-amp amplifies this current and is translated to sound in the headphones. That is the simplest form I have heard of/made/used. I actually built one on my breadboard once to find where wires were in my wall, so that I could drill a few holes for a cable. It worked really well. Should work fine for a science project.

Der Strom
 
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