No. They are not equal.
A rectifier is an electrical device which converts alternating current (AC) to direct current (DC), which flows in only one direction. The process is known as rectification.(Wiki)

Not really. We can only say that the same wire diameter, the conductivity of multi-strand wire is larger than that of a single-strand wire, because the current passes through the surface of the wire and the surface area of the multi-strand wire is bigger.

If you know the square of wire, you can calculate the radius of wire by using that the formula for calculating the circular area, then diameter = 2 * radius ;
Likewise, if you know the diameter of the wire, you can also calculate the square of wire

Step-down transformer: The higher voltage at the input end is converted to the ideal voltage with relatively low output, realizing the voltage reduction.