Space between two concentric conducting spheres of radii $a$ and $b (b > a)$ is filled with $a$ medium of resistivity $\rho $. The resistance between the two spheres will be
JEE MAIN 2019, Diffcult
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$R = \int\limits_a^b {\frac{{\rho {\rm{d}}x}}{{4\pi {x^2}}}} $
$=\frac{\rho}{4 \pi}\left(\frac{1}{a}-\frac{1}{b}\right) $
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