 # a charge Q is distributed over a rod length L.consider a hypothetical cube of length L with the center of cube at one end of the rod.Find the minimum flux of the electric field through entire surface of cube. 12 years ago

in this question a cube is given and we have to minimize the flux through it...

it is given that one end of the rod is at the center and we have to find the other point

so that we can calculate total part of rod inside the cube ....this part will give total amount of

charge inside the cube and thus we will be able to find total flux linked through the cube..

for  other end of rod

if we take a point outside the cube at some distance d ,along the normal of any surface which is passing through center then it will give a point which is at maximum distance L/2 from surface...all points other than this are nearer than L/2  ....so for this point minimum part is inside the cube hence minimum flux .....

therefore total charge insile the cube is Q/2

total flux=Q/2E                           (E is permitivity)