[SOLVED] Value of resistance and impedance

Hi,

From calculations, for a perfect pure resistance have same value of D.C. resistance and A.C. resistance(impedance).

So for same value of D.C. value of voltage and rms value of A.C. voltage, the current must be same for this case.

Q1) Do above sentence are right?

Q2) For impedance, Z=√[(r²)+(x²)] must be greater than the dc resistance(for steady state condition). Below video says that for same amount of voltage of A.C. and D.C. the A.C. current is higher!!! Which means impedance is lower than resistance!!

At 3:33, the current corresponding to the 20V A.C. is 7mA. While at 4:36, the current corresponding to the 20V D.C. is 5.6mA.



How this happened?

Thanks for making me understand in advance.

This is what happens when instead studying electricity due books, you watch underage kids on YouTube making footage of topics that they are clueless about them.

impedance has importance at electrical metrology and measurement of of very low volt and or signals with your Oscilloscope.
impedance it is also important at 6 1/2 multimeter or better ones, for inspection of ultra precise voltage reference because these can not deliver more than 15mA.

He runs a series of tests, watching the Ampere reading through his body as he conducts a range of voltages of both AC & DC. With DC he finds he needs greater voltage before the pain is 'tortuous'.

It seems puzzlzing, then at timepoint 5:48 he states the AC produces a complex impedance due to capacitive properties of the skin. He portrays the concept with a diagram containing capacitors and resistors. It's hard to confirm what is the amount of capacitance generated by his hands on the metal plates. His method appears to be knowledgeable and thorough.

So our skin and flesh is not a pure (ohmic) resistance. Perhaps somebody made a video of tests to measure what capacitance and inductance is involved.

BradtheRad said:

He runs a series of tests, watching the Ampere reading through his body as he conducts a range of voltages of both AC & DC.

Click to expand...

Does he has even kinder-garder Degree as Engineer ?

I do not watch such videos, this is bad influence to my brain cells.
If you need to find more about electrical insulation ? Then start exploring theory of operation of insulation testers.

Considering that the skin resistance varies by several orders of magnitude depending on various conditions, the discussed 20% variation is almost irrelevant. It's not even expectable that the same "test person" reproduces the same skin resistance in succeeding tests. There's surely a certain amount of parallel capacitance in the skin impedance, but I doubt that becomes effective at 50 Hz. Formally, the equivalent circuit with parallel capacitance can explain the reduced AC impedance, in so far Q2 is clearly answered in the you tube video.

I see two more interesting points:

1. As the "experiment" touches the limit values for AC current that can cause ventricular fibrillation, it should never be performed outside a safe clinic lab situation.
2. Besides possible subjective effects, the reasoning for lower AC limit values in safety standards is exactly the risk of ventricular fibrillation.