Question

If a charge is placed outside a closed surface, flux due to that charge inside the surface will be ________

(a) Positive

(b) May be positive or negative, depending on the nature of the charge

(c) Negative

(d) Zero

This question was addressed to me during a job interview.

The query is from Electric Flux in chapter Charges and Fields of Physics – Class 12

Answer 1

The correct option is (d) Zero

Easy explanation: According to Gauss’s principle, if there is no charge bound inside a surface, net electric flux coming out of the surface will always be 0. In this case, the charge is kept outside the surface, so it will generate no field lines and hence no flux inside the surface. The situation will be the same if an electric dipole is placed inside a surface as dipole has equal positive and negative charges; the total charge inside the surface becomes 0.