When a 5 μC charge is enclosed by a closed surface, the flux passing through the surface is φ. Now a -5 μC charge is also placed inside the closed surface. The flux passing through the surface is then

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(4) zero. Given: +5 μC alone gives φ=(5 μC)/(ε₀); then -5 μC is added inside the same surface. Idea: by Gauss's law the flux through a closed surface depends only on the net charge inside it, φ=(qᵢₙ)/(ε₀). Net charge now: qᵢₙ=(+5)+(-5)=0 μC. So the flux is 0/(ε₀)=0. The field on the surface is not zero - lines leave near the positive charge and come back in near the negative one - but as much flux enters as leaves, so the net flux is zero.

When a 5 μC charge is enclosed by a closed surface, the flux passing through the surface is φ. Now a -5 μC charge is also placed inside the closed surface. The flux passing through the surface is then

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