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# A conducting spherical shell is earthed. A +ve charge $+q_1$ is placed at its centre and another +ve charge $+q_2$ is placed outside at a distance d from centre . If the conducting spherical shell is not earthed , then force on $q_2$ is:

$(A)\;zero \\ (B)\;\frac{q_1q_2}{4 \pi \in_0 d^2} \\ (C)\; \frac{q_1q_2}{4 \pi \in_0 (d-R)^2} \\ (D)\;\frac{q_1q_2}{4 \pi \in_0 (d^2-R^2)}$

Charge on outer surface will apply a force on $q_2$
$F= \large\frac{Kq_1q_2}{d^2}$
Hence b is the correct answer.