Two charges of magnitudes `-2Q` and `+Q` are located at points (a,0) and (4a,0), respectively. What is the electric flux due to these charges through a sphere of radius 3a with its centre at the origin ?

Explanation

Gauss. theorem states that the total electric flux linked with closed surface S,
`phi_(E)=E*dS=(q)/(E_(0))`
where, q is the total charge enclosed by the closed Gaussian (imaginary) surface.
The sphere enclosed charge `=-2Q`
Therefore, `phi=(2Q)/(epsilon_(0))" (inwards)"`