Alright I copied this exactly off the sheet, I don‘t even get how to start this problem. gt;lt;If the resistivity of a #12 copper wire (diameter of 80.81 mils) is 10.4 ?-CM/ft), what i the resistivity of #18 gauge copper wire (diameter of 40.30 mils)?
Its just that same! Resistivity is a property of copper and is not dependent on the thickness of the wire. Its like saying fat copper wire is orange, what is the colour of thin copper wire? Obviously still orange. And the same with resistivity.its the same for all time, no matter the shape or whatever of the copper.
The thicker the wire the smaller the resistance to electric current. The longer the wire the greater the resistance. Think about it like water flowing through a hose. The thicker the hose, the more water can flow through at once. For your question, use R pL/A where Rresistance of the wire presistivity of the material, look it up for copper in your book Llength of wire Across sectional area of wire, i.e. the thickness of the wire (you do remember how to calculate the area of a circle when given the diameter right?) By the way, your textbook should tell you about the relationship in the above formula. It is important you understand the relationship and not just copy down the formula.
