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Comment by bozzcl | Hacker News Reader

Reading this, I think I might have been confused about some of these concepts as well. But I had a hard time explaining them to myself.

I wonder, is there any resource online that explains electricity properly in a "for dummies" way? I'd be interested in going through it and seeing what surprises me.

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This article is pretty good. A short summary is that electricity is like a sound wave propagating thru a sea of electrons or protons or something charged.

This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other. They don't bump into each other like atoms in the air, they interact via magnetic field - a mysterious medium that magically appears around charged particles and alters their trajectories. It's the same magnetic field that surrounds bar magnets. Rumors are magnetic field is made of photons, but nobody has been able to see or catch those photons, so they have been renamed into virtual photons. Those special photons don't really exist, but still interact with charges.

> This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other.

Is it any more mysterious then how our planet 'feels' the presence of the Sun, through the gravitational force, despite being 150,000,000 kilometers away?

Do you consider the mechanism through which gravitational effects propagate mundane?

I mean, it is a magical field that seems to surround every single observable object (and some otherwise unobservable ones) that propagates at the speed of light. On that scale of weird, magnetism is not particularly special.

The two are very similar in this regard.

Magnetic field can be derived from electrostatic effects and special relativistic effects. That sounds complicated but both are sophomore level concepts. Sure, the electromagnetic force is mediated by photons, but you don’t need that piece of (graduate-level) knowledge to understand magnetism.

I personally absolutely need that piece of information. I have a simple assumption about the material universe. All interactions rely on touch. Atoms or their sub-particles don't magically interact with each other over a distance.

That's why I still don't understand gravitation, at all. I don't care that we can calculate something. That doesn't tell me what is actually happening.

In a classical sense, no interactions rely on touch and atoms only interact with each other over a distance.

Just think of electricity of water flowing through a pipe. All the concepts are exactly the same.

Electrons = Water molecules

Battery = Water tank

Wire = Pipe

Load = Water mill

Voltage difference = How high tank is from water mill

Amps = Amount of water molecules flowing through pipe

Resistor = Pipe with sand

The problem I have with this sort of popular water analogy is that I don't really have any better intuition on hydraulics or fluid mechanics than I have on electronics. Maybe this has been different in the past when the water analogy was introduced, but I don't see it being very useful at least today.

Let me try with just the analogy of a hose and your thumb.

Water is flowing out of the hose at some rate. If you put your thumb over the end of the hose, you can create a stream of water (of less volume) that shoots out a farther distance because of increased pressure (you can feel this pressure increase in your thumb).

Think of amps as the volume of water, and voltage as the pressure. Power is voltage times current, or pressure times volume of water.

You could squirt a stream of water many feet (raising the voltage), but it's not a very large quantity of water (amps). Conversely, with your thumb off the end of the hose, the pressure (volts) isn't very high (it just flows out at whatever your tap pressure is), but the volume of water is significant (amps).

Curious whether that is any clearer of an analogy?

The thumb is commonly used as an analogy for a resistor because it limits the current. But with the hosepipe it seems to increase the voltage, which a resistor does not do. What you describe (trading current for voltage) is more like a transformer.

Interesting. I spent a lot of time in my childhood playing with water in the sandbox, perhaps that made the analogy more real.

For me it was playing Pipe Mania [0][1].

[0] https://en.wikipedia.org/wiki/Pipe_Mania [1] https://archive.org/details/win3_PipeDr3x

so I guess water in a sandbox is the hydraulic analogy version of scuffing your feet on a shag carpet?

One important difference is that for water we have gravity which is geographically directional at earthly human scales. So "high up" isn't as intuitively visualizable for electric circuits, unless you carefully arrange components so that distance is correlated to voltage.

I don't think voltage is adequately explained like that. It doesn't matter how high a tank of water is, the force pushing it down is exactly the same. I think instead you need to use a pump which can vary the pressure.

The height of the pump increases the distance that the force will do work over (or how much kinetic energy the force will impart to a molecule), akin to how voltage will impart kinetic energy to the electron.

Potential energy due to gravity is mgh. A pump adds more force to g. A tower increases h.

What's nice about the pump is that it removes the special spatial directionality of gravity. In electricity, Earth is a voltage point-of- reference but not a spatial directional reference for computing forces.

The pressure of water at the bottom of a pipe is directly related to the height of the pipe (the term used is "head"). A higher tank means higher pressure.

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