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Question:

Show in the figure are two point charges +Q and -Q inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If σ₁ is the surface charge on the inner surface and Q₁ net charge on it and σ₂ the surface charge on the outer surface and Q₂ net charge on it then :

σ₁≠0,Q₁≠0 σ₂=0,Q₂≠0

σ₁≠0,Q₁=0 σ₂=0,Q₂=0

σ₁≠0,Q₁=0 σ₂≠0,Q₂=0

σ₁=0,Q₁=0 σ₂=0,Q₂=0

Solution:

Net charge inside the cavity is zero. ∴Q₁=0 and σ₁=0
There is no effect of +Q, −Q and induced charge on inner surface on the outer surface hence Q₂=0, σ₂=0