Top resistors

Regarding the oscilloscope waveforms shown at the link Eherdian provided, I'm not sure how they prove anything about anything.

It seems to me that the differences shown for the two orientations mainly involve interplay between the following factors:

1)The difference between the impedance between his fingers and one end of the resistor, and the impedance between his fingers and the other end of the resistor. Each of those impedances being comprised mainly of capacitive coupling between his fingers and the resistive element, plus some fraction of the total resistance of that element.

2)The impedance of the leakage path between the probe's ground and the scope's AC power input. Note that the time scale on the scope is 10 ms/division, from which it can be seen that the "signal" is comprised mainly of 50 Hz (he is evidently in a 50 Hz rather than 60 Hz country).

3)The input impedance of the scope/probe combination (i.e., the impedance that is seen "looking into" the tip of the probe, relative to its ground).

4)The relation between the value of the resistor and the input impedance of the scope/probe combination.

5)The impedance from his fingers through his body and through any path that may exist from there to AC/earth ground.

I see no reason to expect the net result of all of that to be equal for the two orientations, regardless of whether or not the resistor would have directional characteristics when inserted into a circuit. That conclusion would be true even if he managed to grasp the resistor exactly at its mid-point, due to the differences in AC leakage to the probe's ground and its tip.

BTW, although I haven't taken the time to read a lot of the posts in this thread, I happened to notice the one dated 10-22-12 from Larryi. As is almost invariably the case with his posts, it strikes me as being technically plausible, ringing true, and being an important point.

Regards,
-- Al

05-26-13: Rodman99999
Testing capacitors for outer foil, has shown me how much influence a body can have regarding induced noise.

Exactly! And my suspicion is that if he were not holding the resistor in his fingers, he would not have had enough signal to make a meaningful measurement.

Note this statement in the page he links to about the corresponding measurement for capacitors (for which his methodology seems to me to make more sense):

How to do the test with Oscilloscope? Simple by testing both leads, and give some “interference” outside the capacitor (touch by hand or put some electric field interference e.g. high voltage cable, etc). The side with higher noise, means the outer foil.

Regarding

Why would the impedences of the probes, ground wire, etc not remain constant?

They would remain constant, of course, but the impedance of the path between his fingers and the probe's ground would depend on where he was grasping the resistor, and on which end of the resistor the ground clip was connected to. Likewise for the impedance of the path between his fingers and the probe's tip.

Visualize the situation taken to its extreme: He grasps the resistor at one end (without touching the lead). Regardless of the resistor's directionality or lack thereof, it would certainly seem expectable that he would see something different on the scope depending on whether the probe's ground or tip were connected to that end.

If the results were repeatable, and mostly constant, between resistors of the same value; I'd see no reason to doubt the conclusions he's made.

If the measurement were repeated for a number of resistors of the same type and value, and if he grasped each of them at approximately the same position, and if he kept his body located and positioned similarly throughout all of the measurements, I'd expect the results to be reasonably consistent. However, I don't see how those results would say anything about the directional characteristics of the resistor. They would just say something about the net result of the interplay of the five factors I listed in my previous post.

Regarding my previous post, btw, upon re-reading it I realized that the following sentence is flawed. Consider it to be deleted from the post:

That conclusion would be true even if he managed to grasp the resistor exactly at its mid-point, due to the differences in AC leakage to the probe's ground and its tip.

Regards,
-- Al