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# The curved surface area of a sphere of radius $5,$ intercepted between two parallel planes of distance $2$ and $4$ from the centre is

$\begin{array}{1 1}(1)20\pi&(2)40\pi\\(3)10\pi&(4)30\pi\end{array}$

Given radius $r=5$
$a=2$
$b=4$
Required surface area $=2 \pi r( b-a)$
$\qquad= 2 \pi \times 5 \times (4-2)$
$\qquad= 20 \pi$
Hence 1 is the correct answer.