Physics
Physics
Problem
A cube of edge has a point charge at its centre and a point charge located exactly at one of its corners. A third charge of is located outside the cube. (i) Find the net charge enclosed by the cube. (ii) Calculate the total electric flux through the entire surface of the cube. (iii) Assuming symmetry, find the electric flux through each of the three faces that meet at the corner containing the charge.Intuitive explanation
The key to this problem is Gauss's law, which directly links enclosed charge to total flux through any closed surface—no need to integrate. For part (i), only charges physically inside the cube matter; the external charge contributes zero flux. For part (iii), exploit symmetry: the three faces meeting at a corner form a symmetric "wedge," and by symmetry arguments, the flux through each face at that corner relates predictably to the flux from the corner charge alone.
Intuitive explanation
The key to this problem is Gauss's law, which directly links enclosed charge to total flux through any closed surface—no need to integrate. For part (i), only charges physically inside the cube matter; the external charge contributes zero flux. For part (iii), exploit symmetry: the three faces meeting at a corner form a symmetric "wedge," and by symmetry arguments, the flux through each face at that corner relates predictably to the flux from the corner charge alone.