JAMB Physics 2011 Paper

Concept:Young modulus measures how a material resists deformation under stress.It is the ratio of tensile stress to tensile strain.Explanation:Given tensile stress is $7.7 \times 10^{7}\,\mathrm{Nm^{-2}}$.Young modulus is $1.1 \times 10^{11}\,\mathrm{Nm^{-2}}$.Use the relation: $Y = \frac{\text{Tensile stress}}{\text{Tensile strain}}$.Rearrange to make strain the subject: $\text{strain} = \frac{\text{Tensile stress}}{Y}$.Substitute the values: $\text{strain} = \frac{7.7 \times 10^{7}}{1.1 \times 10^{11}}$.Simplify the coefficients and indices: $\frac{7.7}{1.1} \times 10^{7-11}$.This gives $7.0 \times 10^{-4}$.Answer:The strain of the wire is $7.0 \times 10^{-4}$.The correct option is C.