1thats wat I was also thinking
but ans is given as 3CE2
this is a Q from Fiitjee package ,I don't know about the surety of this answer being correct
1.plz explain, what is the electric flux through each surface in a cube when a point charge is kept at one corner of the cube. mag of charge is q.
2. 
each capacitor has capacitance C , find energy drawn from source
Ans. 3CE2
how??
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5 Answers
106Q1. When a charge is kept in a corner of a cube. Imagine there are 8 such cubes (as in the corner atoms of a simple cubic cell) So now the given charge is symmetrically present at the centre of the new system
So, flux through the new system = q/ε
flux through the cube given = 1/8 th of total flux (ex- contribution of corner atom to unit cell) = q/8ε
Now flux through each surface will be (q/8ε)/6 = q/48ε
NOTE (this is the average flux through each surface)
Different surfaces will have different flux through them. The three surfaces in contact with the charge q will have ZERO flux through them as E.S = 0 angle being 90°
I am not pretty sure abt this but i think the flux through the remaining three surfaces will be q/24ε each
106Q2. Net capacitance of the system = 3C/2 . So, Energy drawn from the source = CV2 = 3CE2/2
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