A point charge +Q is located on the x axis at x = a, and a second point charge -Q is located on the x axis at x = -a.A Gaussian surface with radius r = 2a is centred at the origin.The flux through this Gaussian surface is:
A)zero because the negative flux over one hemisphere is equal to the positive flux over the other.
B)greater than zero.
C)zero because at every point on the surface the electric field has no component perpendicular to the surface.
D)zero because the electric field is zero at every point on the surface.
E)none of the above.

Question

Quizplus · Accepted Answer

The electric field of a point charge is spherically symmetric, so the flux through a Gaussian surface surrounding the charge is proportional to the surface area of the Gaussian surface. In this case, the Gaussian surface is a sphere with radius r = 2a, so the flux through the surface is proportional to 4π(2a)^2 = 16πa^2. Since the electric field of a point charge is proportional to 1/r^2, the electric field at the surface of the Gaussian surface is proportional to 1/(2a)^2 = 1/4a^2. Therefore, the flux through the Gaussian surface is proportional to 16πa^2 * 1/4a^2 = 4π, which is greater than zero.

A Point Charge +Q Is Located on the X Axis