(adsbygoogle = window.adsbygoogle || []).push({}); A point charge [itex]q[/itex] is located at the center of a thin ring of radius [itex]R[/itex] with uniformly distributed charge [itex]-q[/itex]. Find the magnitude of the electric field strength vector at the point lying on the axis of the ring at a distance [itex]x[/itex] from its center, if [itex]x \gg R.[/itex]I managed to solve the problem to find the electric field strength as a function of x:

[tex]

E(x) = \frac{1}{4\pi \epsilon_0}\left [\frac{q}{x^2} - \frac{qx}{(R^2+x^2)^{3/2}}\right ][/tex].

However, I'm having some troubles with the [itex]x \gg R[/itex] part of it. I assumed that this meant that [itex]R \rightarrow 0[/itex], and my function, when R was set to zero, became zero. But the answer says

[tex]

E = \frac{3qR^2}{4\pi \epsilon_0 R}

[/tex]

First of all, I don't understand why the R is still there. Second, I don't understand why letting R go to zero is incorrect. If someone could please clarify why the answer is not zero, but is instead this last expression, I would appreciate it.

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# Homework Help: Electric field problem

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