A copper wire of length 4.0 m has a uniform cross-sectional area of 4.5 × 10⁻⁷ m². A tensile force of 18 N is applied to the wire, causing it to extend by 1.4 mm up to its limit of proportionality.

On Fig. 4.1, draw a line to show how the stress varies with the strain for the wire up to its limit of proportionality.