A charged shell of radius R carries a total charge Q. Given `phi` as the flux of electric field through a closed cylindrical surface of height h, radius r & with its centre same as that of the shell. Here centre of cylinder is a point on the axis of the cylinder which is equidistant from its top & bottom surfaces. which of the followintg are correct.

Options

A. If h gt 2R and r gt R then `phi =Q/epsilon_0`
B. If `h lt (8R)/5` and `r=(3R)/5` then `phi=0`
C. If h gt 2R and r= `(4R)/5` then `phi=Q/(5epsilon_0)`
D. If h gt 2 R and r= `(3R)/5` then `phi=Q/(5epsilon_0)`

Answer

A, B, D

Explanation

Option (a) - Cylinder encloses the shell completely hence electric flux is `Q//epsilon_0`, Hence option (a) is correct.
Option (b)- If h = 8R/5 then cylinder is perfectly enclosed by shell, thus `phi` =0 hence option (b)is correct.

Hence option (c) is wrong .
Option -(d)
In previous diagram if we use 3R/5 instead of 4R/5 then we can write the following equation :
`phi=(2Q)/(2epsilon_0)(1-cos37^@)=Q/(5epsilon_0)`
hence option (d) is correct.