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Asked in GUJCET 2017 · Gauss's law and enclosed charge
Idea: Gauss's law, φ=(qᵢₙ)/(ε₀). Only the charge inside a closed surface counts; a charge outside sends in exactly as many field lines as it takes out.
Surface P encloses only -q; the +2q beside it is outside.
φ_P=(-q)/(ε₀)=-q/(ε₀)
Surface Q encloses only +q; the -q beside it is outside.
φ_Q=(+q)/(ε₀)=q/(ε₀)
So the fluxes are -q/(ε₀) and q/(ε₀).
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