KCET 2026 Physics Solved Paper

Concept:Use Gauss's law and symmetry, since the charge lies on an edge shared by 4 identical cubes.Explanation:Gauss's law states that the net flux through a closed surface is:$$\Phi = \frac{q_{\text{enclosed}}}{\varepsilon_0}$$The charge $Q$ is at $B$, the midpoint of an edge of the cube.Hence, $Q$ is not completely inside this cube alone.In a cubic arrangement, an edge is common to 4 identical cubes.Imagine these 4 cubes joined together to form a larger closed surface.This combined surface fully encloses the charge $Q$.So the total flux through all 4 cubes is:$$\Phi_{\text{total}} = \frac{Q}{\varepsilon_0}$$By symmetry, this total flux is shared equally by the 4 cubes.Thus, the flux through the given cube is:$$\Phi_{\text{cube}} = \frac{1}{4} \times \frac{Q}{\varepsilon_0}$$$$= \frac{Q}{4\varepsilon_0}$$Answer:The total electric flux through the faces of the cube is $\frac{Q}{4 \varepsilon_{0}}$.