# Measuring time delay before charged plates repel

1. Feb 26, 2014

### johne1618

Imagine two parallel conducting plates set at a distance of several meters.

If one charges the two plates simultaneously then one would expect a small delay before they started repelling each other due to the time it takes changes in the static field to propagate from one plate to the other.

Could one experimentally measure such a delay?

I guess it would be so small and the deflection of the plates would be so weak that the effect would be unmeasureable.

I don't know if one could use electronic field detectors rather than rely on the mechanical deflection of the plates.

2. Feb 26, 2014

Staff Emeritus
How do you plan to charge the plates instantaneously?

3. Feb 26, 2014

### johne1618

I was imagining that the separation of the plates was much larger than their dimensions so that the time it takes to charge the plates is small compared to the delay time in the electrostatic repulsion.

I guess this would mean that the repulsion would be very weak in that case.

4. Feb 27, 2014

### dauto

That's a very hard experiment to perform successfully. The fields propagate at the speed of light (because it is light)

5. Feb 27, 2014

### johne1618

I've looked up the specifications of an Electric Field Meter (JCI140 Field Mill Static Monitor from Chilworth Technology) and the manufacturers say that it can measure a surface voltage of 1 volt at a distance of 1/10 meter.

Therefore if one charged up an electrode to 1 MV then according to the inverse square law it should be just detectable at a distance of 100 meters.

The time delay for light to travel 100 meters is about $3\times 10^{-7}$secs which would be easily measured with a GHz electronic oscillator.