When to use Archimedes theorem to calculate

When to use Archimedes theorem to calculate

Archimedes theorem is that f = liquid density * g * V row
We have just learned it
It's buoyancy
This theorem holds as long as the object is immersed in liquid
If an object floats on a liquid, f = g, Archimedes' law is not necessary. Of course, it doesn't matter if it is used

Why should resistance wire be coated with insulating layer in sliding rheostat

Because the resistance wires are tightly wound together, if the insulation layer is not applied, the whole wire will be connected into a large area, and the resistance will be reduced
When there is insulating layer, although the resistance wire is close to each other, it is still a very long one

Where is the insulating paint removed from the resistance wire of the sliding rheostat? Why is it removed?

The insulating paint has been scraped away from the place where the slide contacts
The outer layer of the resistance wire must have insulating paint to prevent the winding resistance wires from short circuit. The sliding rheostat is connected to one end of the resistance wire and the slide, so the resistance wire must be connected with the slide
The place where the sheet metal reaches
Because we need to connect the resistor

The purpose of sliding rheostat is to wind many resistance wires on the insulating cylinder_______

In this way, the resistance can be changed to change the voltage protection circuit (personal view)