Electronic – Calculate resistance of coil/inductor made of PCB traces

Protoboards are up to you how to use, if it works, it works.

The three common methods of using them is using jumper wire, solder bridges, or using leads. Or all three, depending on your needs.

Solder bridges take a lot of solder, especially long ones. They are good for two or three adjacent points.

Using the leads, or bare wire, is great for straight lines and buses, using less solder than solder bridges.

And jumper wire is best for when you can't/don't want to go around an existing solder joint.

It all really boils down to what you need. Of course, solder bridges can be very sloppy if you don't have practice at them. And using too many jumper wires or bare leads looks ugly and not well thought out. But this is your project, you can figure out how to mount them, and what's acceptable or not.

If you need much of either, what you really want to do is think about the placement of your components, move stuff around to minimize the need to use jumpers or long bridges.

Not an easy problem to solve without modeling software. You have probably noticed that water has a value of resistivity rather than resistance, stated in ohm-meters. This is because the ratio of voltage to current is proportional to the distance and inversely proportional to the cross section of the water.

Take a look at the two images below and you can begin to see the problem. The voltage distribution is shown in figure 12.4 and the current density in 12.5. The voltage varies between any two points in the current path, and the current density would also vary if the graph had higher resolution. Then consider that this is a model of a thin disc, and so there is a third dimension that would be present in real life to add complexity. The boundary might be conductive, which would change everything. Finally, the surface area of the conductor in the water will make a difference - the model uses point sources.

Your best bet is to place the water in a vessel of known geometry with electrodes of know geometry and do some modeling or some empirical testing. Bare copper may form a non-conductive oxide layer.