Hi, this is silicon soup.
In my last video, I explained that KVL failed in the changing magnetic field.
The simplest and the most profound example is that voltage measured along the wire is
0, but voltage across the loop has a non-zero value induced by the changing magnetic flux.
This phenomenon is well understood in advanced electromagnetism, but it can still be unintuitive
and even shocking to most people.
So
now I am going show you an experiment that matches up with the theory, in hope that it
will help you to accept the reality, and have a better understanding of electromagnetism.
Here I have a single loop acting as the secondary winding of a transformer, and the changing
magnetic flux is derived from a toroidal transformer.
From the zoom-out photo, you can see that the voltage across the two ends is 0.121V, but the voltage
across each segment is zero.
How can all the 0 volts be added up to 0.121V?
This is indeed a shocking result of KVL failure, and if you don't appreciate that, I don't
know what to say.
So let's zoom in the photo to have a better view of the readings.
This is the meter reading for voltage across the two ends, 0.121V.
This is the voltage a cross the wire segment, 0 volt, across another wire segment 0V, and
another wire segment, another wire segment 0V again.
Unfortunately due to the limited number of multimeters I had access to, the first and
the last segments were not measured simultaneously, but I can assure you that they were 0 volts
too when they were measured independently.
In case you are skeptical of the photo, here are the video clips of the experiments.
When I turned on the supply, the voltage appeared across the terminals, and settled down to
0.121V AC after the voltmeter filtered off the transience.
The other meters read 0 volts.
Notice that I correctly set the meters to the AC mode, so that the 0V readings are indeed
the actual AC voltage across the wire segment.
I have to emphasize this, because should the meter be set to the DC mode by mistake, then the
0VDC does not imply the absence of the AC voltage, and this is to assure you that the
AC voltages were NOT missed out in the measurement.
In case you think the 0V reading is due to the probing clip having no contact with the
measuring point, then this is what happen when the clip is removed from the contact.
You can see the probing wire becomes floating and picks up electric-field in the air and
gives jumping numbers.
So the 0V readings turn out to be confirmation of good contacts.
If you know ohms law, 0V across a 0 ohm wire is normal, and expecting otherwise is ridiculous.
Notice that when the probe was moved to contact the other end opposite, the induced voltage
appeared again.
Now, you might be cracking your head for an explanation for this phenomenon.
Sure, there is explanation for this, as in my earlier videos.
Whatever explanation you might have, the point is, you should not deny that KVL has exception,
as demonstrated in this measurement.
Of course, I have seen many ridiculous arguments such as these meters were not measuring the
actual voltages, and so they could not disprove KVL.
But physics tells us a voltmeter measures the total electric-field accumulated along
the probing loop, so what it measures is consistent with the definition of voltage given by IEC.
In other words, this setup is a legitimate way of verifying KVL, and it does demonstrate
a case of KVL exception.
Thank you for watching.
If you find the result surprising, share it with your friends.
If you think I am crazy, share it with someone more knowledgeable and discuss about it. See you again.