Re: To All The Pseudo Engineers 2

On Wed, 15 Jan 2025 10:55:43 +0000, Farley Flud wrote:

 
Often, when an electronic device is plugged into the power
outlet there will be sparking.
 
Explain, using explicit mathematical equations, why this
happens.
 

Ha!  All of the fat mouths have failed.

This is freshman stuff.  Very basic.

I shall explain.

Every circuit has inductance, even if the inductance is totally
parasitic.

The equation for the voltage across an inductor is the following:

delta V = -L * dI/dt

So the voltage is proportional not to the current (I) but to the
rate of change of current (dI/dt).

Thus, when a circuit is "plugged in" or connected to the mains power
source, the current begins to flow from zero.  The rate of change
(dI/dt) is extremely large and so is the voltage.  The voltage is
so large that it causes a dielectric breakdown of the air, i.e. a
spark (a mini lightning bolt).

Actually, due to the electric field of the mains, the current actually
begins to flow before contact is made.  The spark will jump across
the small gap.

At times, the spark is so hot that it can cause pitting of the metal contacts.

This phenomemon will happen all the time.  There is no way to avoid it,
other than perhaps to make contact at zero volts and then turn the
voltage up after contact is made.


Oblinux:

I say so.


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