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Name: Justin
Status: student
Age: 11
Location: N/A
Country: N/A
Date: 1999-2001


Question:
I have an experiment for school about lighting up a pickle. You insert a wire (from a split electrical cord) into each end of the pickle. Then you plug the cord into the electrical outlet. The pickle lights up. Why?


Replies:
Hello,

I checked into the problem of the glowing pickle. You are right and I was wrong. Pickles do glow when a sufficiently high voltage is applied across them.

I read about the issue a little bit and the explanations for it. However, careful experiments with proper tools must be carried out to validate the explanation.

First, let's talk about electrical arcs (sparks). A spark is simply a sudden and massive flow of electrons. If we apply a voltage across a pair of metal (or other suitable) rods (let's call the rods electrodes) and bring the electrodes together but not touching, a spark may be generated. The distance between the two electrodes (the "gap") at which an electric arc is formed depends on the voltage applied, the air (or the medium) between the electrodes, etc. The more electrically conductive the medium between the electrodes, the smaller the gap for a spark to happen. For example, lightning can occur across shorter paths if there is moisture in the air (wet, humid air is more conductive than dry air). One other bit of useful information is that sparks are hot; in fact, the temperature can easily exceed thousands of degrees. If two metal electrodes (with 120 V across them) are brought close enough to each other to initiate a spark, the tip of the electrodes can melt or evaporate. This property of sparks is used in welding. With an AC power supply, sparks generally come and go as the voltage goes through its maximum/minimum and zero.

One last observation is that if one pours some regular salt on the spark, one would see an orange color light, of the same color as some orange street lights (both have sodium in them; when sodium atoms are excited, they give back the applied energy by radiating their characteristic color).

Now, what do these all have to do with a glowing pickle?

Well, as you apply a voltage across the pickle, the pickle begins to conduct electricity. You can verify this using an ammeter to measure the current. The pickle gets warm/hot (just as in an electric stove when current is passing through it). A layer of vapor is generated around the electrodes; it acts to insulate and cut off the flow of electricity. Essentially, a gap is created between one of the electrodes and the rest of the pickle. Current does not flow anymore and no heat is generated. The temperature around the electrodes goes down and the vapor layer gets thinner until it is thin enough for an arc to form. It is this spark that, when in the salty environment of the pickle, generates the orange colored light. This is a plausible explanation. Please look at the following website for some interesting information as well as for a movie of a glowing pickle:

http://www.geocities.com/CapeCanaveral/Launchpad/6603/glowing.html.

One possible problem with this explanation is that from the movie it SEEMS that the sparks are mostly near the pickle's skin. It may, however, be that the skin provides the lowest resistance path (i.e., it is more conductive) and current preferentially goes from the electrode to the nearest location on the pickle skin. If I were to repeat this experiment, as one of the tests, I would peel off the skin and try it that way.

My guess is that if the above explanation is not exactly correct, it is very close to describing what is happening. And as a final note, one must be very careful about conducting this experiment. Electrocution and skin/eye injury resulting from a pickle that splatters are REAL dangers. This is not a home project.

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439



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