If the percentage error in measuring the surface area of a sphere is $\alpha \%$, then the error in its volume, is |
$\frac{3}{2} \alpha \%$ $\frac{2}{3} \alpha \%$ $3 \alpha \%$ none of these |
$\frac{3}{2} \alpha \%$ |
Let r be the radius, S the surface area and V the volume of the sphere. Then, $S=4 \pi r^2$ and $V=\frac{4}{3} \pi r^3$ Let $\Delta r, \Delta S$ and $\Delta V$ be the errors in r, S and V respectively. Then, $\Delta S =\frac{d S}{d r} \Delta r$ and $\Delta V=\frac{d V}{d r} \Delta r$ $\Rightarrow \Delta S =8 \pi r \Delta r$ and $\Delta V=4 \pi r^2 \Delta r$ $\Rightarrow \frac{\Delta S}{S}=\frac{8 \pi r}{4 \pi r^2} \Delta r$ and $\frac{\Delta V}{V}=\frac{4 \pi r^2 \Delta r}{\frac{4}{3} \pi r^3}$ $\Rightarrow \frac{\Delta S}{S} \times 100=2\left(\frac{\Delta r}{r} \times 100\right)$ and $\frac{\Delta V}{V} \times 100=3\left(\frac{\Delta r}{r} \times 100\right)$ $\Rightarrow \alpha=2\left(\frac{\Delta r}{r} \times 100\right)$ and $\frac{\Delta V}{V} \times 100=3\left(\frac{\Delta r}{r} \times 100\right)$ $\left[∵ \frac{\Delta S}{S} \times 100=\alpha\right.$ (given)$]$ $\Rightarrow \frac{\Delta V}{V} \times 100=3\left(\frac{\alpha}{2}\right)=\frac{3}{2} \alpha$ |