Let’s Get Physics-l: Kirchhoff’s First Law

(Please note: The Characters used in my examples are property of DC comics and in no way belong to me. I am using them to help convey the theory I’m writing about. Thank you)

Gustav Kirchhoff is best known for his contributions to fundamental theories involving electrical circuits, spectroscopy and black-body radiation. The bit we are going to be focusing on is the electrical circuits aspect of his career, namely his first law.

Also known as a the principle of conservation of charge, Kirchhoff’s first law states that:

The charges flowing into a junction are equal to a charge leaving it

The same applies to current as it is the rate of flow of charge.

Time for another superhero example! Terror has descended on Star City (I appreciate both DC and Marvel comics, as you well know) with Reverse Flash on the run (Noted, he’s always on the run). Our good friend the Flash is, well, quick to respond to calls to stop Reverse Flash in his tracks and manages to find the Reverse Flash along a random street. For the sake of this example, let’s say they are running side by side at a combined speed of 2000 ms^-1, 1000ms^-1 individually. They are running along a street when it suddenly breaks into two separate streets. Flash goes down one street at a slightly slower speed of 950 ms^-1. Now, if we apply Kirchhoff’s first law to this scenario, Reverse Flash would be travelling down the other street at 1050 ms^-1. The sum of their speed before entering the junction is equal to that when exiting it.

Now, in reality, we would substitute speed here for amps/coulombs, the streets for wires and our hero/villain for charge carriers but it just about illustrates the point I’m trying to convey. According to Kirchhoff’s first law Charge/Current cannot be destroyed thus the current/charge entering a junction is equal to that exiting the junction.


Kirchhoff’s first law states that the charge/ current entering a junction is equal to the current/charge exiting a junction – The Principle of Conservation of Charge.

There we have it, Kirchhoff’s first law. Not going to deny, it feels rather fulfilling being able to say that I know what it is and I hope you can now experience that as well. I will more than likely recap this in a future post (Kirchhoff’s Second Law, the glorious sequel) so that should be intersting. As always, if you have any feedback, thoughts or questions then please leave them in the comments.

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