In order to measure the diameter of the thin copper wire, a student arranged the thin copper wire tightly on the pencil for 30 turns, as shown in the figure. From the figure, we can see that the length of the coil is______ Cm, the diameter of copper wire is______ cm．

In order to measure the diameter of the thin copper wire, a student arranged the thin copper wire tightly on the pencil for 30 turns, as shown in the figure. From the figure, we can see that the length of the coil is______ Cm, the diameter of copper wire is______ cm．

There are 10 small grids between 1cm on the scale, so a small grid represents 1mm, that is, the graduation value of the scale is 1mm; the left side of the coil is aligned with 10.00cm, the right side is aligned with 14.1cm, the estimated reading is 14.10cm, so the width of the coil is L = 14.10cm-10.00cm = 4.10cm. The diameter of the copper wire is d = ln = 4.10cm30 ≈ 0.14cm

As shown in the figure, two groups of coils are wound on the iron core, and ab conductor in uniform magnetic field is found on the smooth metal guide rail

According to Lenz's law, the area of AB moving to the right increases, which indicates that its magnetic flux is decreasing
That is, the current is weakening
So choose BC

Use a piece of wire on the pencil and wind it for 20 turns. As shown in the figure, use a scale to measure the width of 20 turns______ Mm. The diameter of this wire is______ Mm

It can be seen from the figure that l = 2.00cm = 20.0mm, n = 20, so d = ln = 20.0mm20 = 1.0mm