You stand at location A, a distance d from the origin, and hold a small charged ball. You find that the electric force on the ball is 0.056 N. You move to location B, a distance 2d from the origin, and find the electric force on the ball to be 0.028 N. What object located at the origin might be the source of the field? (Select all that apply.)(a) a point charge(b) a dipole(c) a uniformly charged rod (for d ≪ L)(d) a uniformly charged ring (for d ≪ R)(e) a uniformly charged disk (for d ≪ R)(f) a uniformly charged hollow sphere(g) none of the above

a uniformly charged rod (for d ≪ L)

Explanation:

Given:

- Force at point d is F_ 1= 0.056

- Force at point 2d is F_ 1= 0.028

Find:

 What object located at the origin might be the source of the field?

Solution:

- We see that as the distance is doubled that force is half. So we are looking at an object whose electric Field strength is inversely proportional to the distance from the source.

- A point charge, dipole, and hollow sphere all are related by distance being inversely proportional to squared of the distance.

- A charged ring with R >> distance will give us E = 0.

- A charged disc with R >> distance will act like a uniform infinite sheet of charge which in dependent of distance.

- A uniformly charged infinite rod is Electric field is proportional to inverse of distance from the charge. We can see that from a application of Gauss Law.  

this is poiselle's equation from fluid mechanic in physics. mech eng