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Asked in RS Academy GUJCET booklet · Gauss's law and enclosed charge
Given (from the figure): +q and -q lie inside the closed surface S; 2q and q lie outside it.
Idea: Gauss's law, Φ = (q_enc)/(ε₀); only the charge inside the surface counts.
q_enc = (+q) + (-q) = 0
Φ = 0/(ε₀) = 0
The outside charges 2q and q do change the field on S, but every one of their lines that enters S also leaves it.
So the flux through the closed surface is zero.
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