Bio Lab Question (Field Strength)

Aug 22, 2008 6 Replies

If I drive an A/C voltage into two parallel wires taped to either side of a magnolia leaf 4cm apart, how do I calculate/measure the electrical field strength?



Can I just put JFET probes on either side of the leaf, 1cm apart, and measure the voltage between the probes?



How would I calculate it the field strength? 100V p-p signal driven into the wires is a 25V/cm field strength?


At 100 volt and a solid contact your leaf would not last very long , it would start smoking. If it does not smoke, you cannot calculate the field strength distribution, because of the veins in the leaf local leaf resistance will vary all over the place, and be unpredictable. A measuring probe would have to have a very small tip, which would have to be shielded for all but the last .2 mm. A fet probe would not really be needed, the leaf has a rather low resistance, just use a very sharp needle tip. No need for 100 volt, voltmeters are happy to measure millivolts, so a supply voltage of ~5 volt is oke. Dont wait to long with your measurements, because the connections will degrade due to electro-chemical reactions at the contact places.

Sorry!! I am using insulated wires. No current will be directly conducted through the leaf.

Then there will be no mesurable field.

Incorrect. There would be no MAGNETIC field if there is no current through the leaf, but

100V across two insulated plates most definitely results in a measurable electric field between the plates.

But what the leaf's contribution to this is supposed to be, I haven't a clue.

What, exactly, are you trying to do here?

Bob M.

I want to apply an electric field to the leaf, ~1V/cm, ~100KHz, for 30 days, and then observe biological effects.

Then you're going about it the right way; the leaf would be positioned between two electrodes, which then would be driven to the appropriate potential to produce the desired field strength. You can calculate the expected field strength given the configuration and spacing of the electrodes, but may want to employ a field strength meter to more readily set this and check it.

May I ask what you are expecting will happen?

Bob M.

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