Question

A point charge Q is kept near the corner D of a cube (inside cube) as shown in figure.

• A. Flux crossing Face ABCD is zero
  
• B. Flux crossing face ABCD is $\frac{7R}{2u{ϵ}_0}$
• C. Flux crossing Face ADEH is $\frac{7R}{8{ϵ}_0}$
• D. Flux crossing Face ABGH is $\frac{R}{2u{ϵ}_0}$ wether charge R just inside or just outside of cube near corner

Answer 1

Answer: (B), (D)

The correct options are
B Flux crossing face ABCD is $\frac{7R}{2u{ϵ}_0}$
D Flux crossing Face ABGH is $\frac{R}{2u{ϵ}_0}$ wether charge R just inside or just outside of cube near corner

The flux passing through the faces BCFG, EFGH, ABGH can be approximated as $3\times \frac{Q}{24{ϵ}_0}=\frac{Q}{8{ϵ}_0}$
So, flux passing throughthe remaining surfaces ABCD, AHED, CDEF will be $\frac{7Q}{8{ϵ}_0}$
$\therefore$ Flux crossing face ABCD is $\frac{7Q}{24{ϵ}_0}$

Flux crossing face ABGH is $\frac{Q}{24{ϵ}_0}$ .