JEE MAIN - Physics (2019 - 10th April Evening Slot - No. 16)
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 :
$${\rho \over {2\pi }}\left( {{1 \over a} + {1 \over b}} \right)$$
$${\rho \over {4\pi }}\left( {{1 \over a} + {1 \over b}} \right)$$
$${\rho \over {2\pi }}\left( {{1 \over a} - {1 \over b}} \right)$$
$${\rho \over {4\pi }}\left( {{1 \over a} - {1 \over b}} \right)$$
Explanation
$$R = \int\limits_a^b {{{\rho \,dx} \over {4\pi {x^2}}}} $$
$$ = {\rho \over {4\pi }}\left( {{1 \over a} - {1 \over b}} \right)$$
$$ = {\rho \over {4\pi }}\left( {{1 \over a} - {1 \over b}} \right)$$
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