Resistance calculation?

[Ohm*mm²/m] 0.0171 = copper coefficient of resistivity.

The resistance R of a copper wire with the length l can be calculated with the following formula:

R=(l*p)/A

where

R is the resistance of the conductor in Ohms

l is the length of the conductor in meters

ρ is the electrical resistivity (also known as the specific electrical resistance) of a conductor.

A is the cross-sectional area, measured in square millimeters

π is the mathematical constant

d is the nominal diameter of the wire in millimeters

Resistivity ρ

http://hyperphysics.phy-astr.gsu.edu/hbase/electri...

According to the website above, resistance is directly proportional to the length and inversely proportional to the cross sectional area.

find the new resistance of a Copper wire of original diameter 1cm with an original resistance of 0.15 ohms, after the wire diameter is reduced by 50%

Area = pi * r^2

The new radius is ½ the original radius.

New area = pi * (r/2)^2 = ¼ *pi * r^2

The new area is ¼ the original area, so the new resistance is 4 times the original resistance.

0.15 * 4 = 0.6 ohms