How to measure the diameter of 100cm wire

How to measure the diameter of 100cm wire

1. Direct measurement with spiral micrometer;
2. Vernier caliper direct measurement;
3. The diameter of each wire is divided by the total number of wires;
4. Weigh out the weight of 100cm wire, calculate its volume according to its density, calculate its cross-sectional area according to its length, and calculate its diameter according to the area of circle

What is the method used to measure the diameter of a thin wire with a millimeter scale

Take a few turns of the wire, measure the length with a scale, and divide the total length by the number of turns

In a hurry As shown in the figure, Mn and PQ are two parallel smooth metal rails placed in a vertical plane and long enough, with a distance of 2l
 
Supplementary picture

1. The induced electromotive force E = B (2L) V0 = 2blv0. The induced current I = E / (2R) = blv0 / R. this is the current through resistance R. if the voltage at both ends of the resistance u = IR = blv02 and the oil droplet moves at a constant speed, the electric field force is equal to gravity, Qu / L = mg, then M = Qu / LG