WAEC Physics 2019 Paper

Concept:Heating a solid causes it to expand in all dimensions, so the area expansion is calculated using twice the linear expansivity.Explanation:The new area is given by $A_2 = A_1(1 + 2\alpha\Delta T)$. Initial area: $A_1 = 4 \times 3 = 12\ \mathrm{cm}^2$. Temperature rise: $\Delta T = 100\ \mathrm{K}$ since a change of $100^\circ\mathrm{C}$ equals a change of $100\ \mathrm{K}$. Linear expansivity: $\alpha = 1.2 \times 10^{-5}\ \mathrm{K}^{-1}$. Area expansivity: $2\alpha = 2.4 \times 10^{-5}\ \mathrm{K}^{-1}$. Increase in area: $\Delta A = A_1 \times 2\alpha \times \Delta T$. So, $\Delta A = 12 \times 2.4 \times 10^{-5} \times 100 = 0.0288\ \mathrm{cm}^2$. New area: $A_2 = 12 + 0.0288 = 12.0288\ \mathrm{cm}^2$. This matches option C.Answer:$A_2 = 12.0288\ \mathrm{cm}^2$ Correct option: C.