(a(i))[1]
State the name of a suitable instrument for measuring the diameter of the wire.
(a(ii))[2]
For the diameter measurement, state how random errors can be reduced when the instrument from part (a)(i) is used.
(b(i))[1]
The stress $\sigma$ in the wire is found from the expression $\sigma = \frac{4F}{\pi d^2}$. Show that $\sigma = 1.99 \times 10^{8}\,\text{N m}^{-2}$.
(b(ii))[2]
Find the percentage uncertainty in $\sigma$.
(b)
The stress $\sigma$ in the wire is found from the expression $\sigma = \dfrac{4F}{\pi d^2}$.
(b(iii))[2]
Use the result from (b)(i) and your answer in (b)(ii) to find the value of $\sigma$, together with its absolute uncertainty, to a suitable number of significant figures.