THIS IS THE QUESTION EDWARD Electric charge and coulumb law,help me get my home work pls with this,A & B?

Question

'A.'show that at large distance from the ring (x>>a),the electric field along the axis approach that of a point charge of magnitude Q.

where electric field (E=Kxq/(x2+a2)3/2

'B'a disk of radius R has a uniform charge per unit area () .calculate the electric field along the axis of the disk.

Answer 1

A

For the uniformly charged ring the E - field in general  is

Ex=k q x/ (x^2 +R^2)^3/2 (see ref 1 if you want to derive the equation)

As x being much larger than R (x>>R

Ex=k q x/ (x^2 )^3/2

Ex=k q /  x^2   just like for the point charge!

B.

Similar to A. (See ref 2)

I hope it was useful.

Answer 2

Please see

http://answers.yahoo.com/question/index;...