24isnt 2nd easy ???
ΔV=2000-1800=200=kQ/100
Ques1) 
An infinite wire having charge denisty λ passes through one edge of the cube having edge length ' l ' .The wire is just inside the cube.
Find the
(a)Total flux passin through the cube.
(b) Flux passing through the surfaces which are at contact with the wire.
(c) Flux passing through the surfaces which are not in contact with the wire.
Ques2) 
It has been experimentally observed that the elctric field in a large region of earth's atmosphere is directed vertically downward. At an altitude of 300m, the electric field is 60 V/m. At an altitude of 200m, the electric field is 100 V/m.Show that the net amount of charge contained in the cube of 100 m edge, located between 200m and 300m altitude is 3.54 µ C.
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12 Answers
1the charge on the wire which is in contact is λl,
if make 3 other similar cube touching the same part of the wire then it will be a cube of length 2l,
and net flusk coming out wll be λa/ε now the flusk through surfaces(of the smaller cube) in contact with the wire is will be zero because E.da will be zero there,
flusk will only pass through the outer surfaces(for the smaller) hence flusk through each surface will be λl/8ε n we r concerned 2 surfaces hence flusk through cube will be λl/4ε..
106If the wire is just inside the cube then the flux is λl/ε
The answers are correct if the wire is on the edge of the cube
62Yes asish you are correct.. so is sahiba...
if the charge is exactly on the wire then the flux will be 1/4th
otherwise it will be λl/ε
106but sir the question mentions
The wire is just inside the cube.