Well, 3 questions actually. See below.
Please show me the working out and not just the answers.
Thanks in advance!
For question 3 you are told that the resistance varies linearly with length and inversly as the square root of the diameter. That means there is a constant $\displaystyle k$ (other things being equal) such that:
$\displaystyle R=\frac{k l}{\sqrt{d}}$
You are given the resistance, 30.9 Ohms of a 850 mm length of 0.122 mm diameter wire so:
$\displaystyle k=\frac{30.9\sqrt{0.122}}{850}$
when resistance is given in Ohms and length and diameter in mm.
Now you know $\displaystyle k$ you can use the first equation to find the resistence of any wire of the same material.
RonL