(a)[1]
Explain what plastic deformation means.
(b(i))[2]
Calculate the breaking force for a copper wire with a uniform cross-sectional area $1.54 \times 10^{-6}\,\text{m}^2$ and a length of $1.75\,\text{m}$. Its breaking stress is $2.20 \times 10^8\,\text{Pa}$, and the Young modulus of copper is $1.20 \times 10^{11}\,\text{Pa}$.
(b(ii))[2]
A stress of $9.0 \times 10^7\,\text{Pa}$ is exerted on the wire. Calculate the extension.
(c)[1]
Explain why it is not suitable to use the Young modulus to determine the extension when the breaking force is applied.