The length of the wire can be obtained by knowing the cross section, density and mass of the wire That is why it is best to deduce other formulas, such as known wire length, cross section mass, metal density, etc

The length of the wire can be obtained by knowing the cross section, density and mass of the wire That is why it is best to deduce other formulas, such as known wire length, cross section mass, metal density, etc

Analysis: wire is cylindrical shape
Cylinder volume formula v = SL density formula: P = m / v = m / (SL)
So the length of cylinder L = m / (SP)

There is a very long and thin wire, which looks like hair. How to measure the diameter of the wire roughly with a scale? Write down what you do

With a cylindrical object (such as a pen), wind the wire on it for a few turns, preferably to the width that can be measured by the scale, then measure it, count several more turns, and divide it
For example: after 10 turns, if the measurement is 1cm, use 1cm / 10

There is a pencil and a scale. How can we measure the diameter of a roll of thin wire with them?

If the length L and the number of turns n are measured, then the diameter is L / n