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Electric Field Due To A Uniformly Charged Ring - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

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  • 12 Questions around this concept.

Concepts Covered - 1

Electric field on the axis of a charged ring

In this concept we are going to derive the electric field due to continous charge on a ring -

                                                         

In this one should notice that there symmetry in this situation. Every element dq can be paired with a similar element on the opposite side of the ring. Every component \vec{dE} perpendicular to the x-axis is thus cancelled by a component \vec{dE} in the opposite direction.
In the summation process, all the perpendicular components \vec{dE} add to zero. Thus we only add the dE_x components, which all lie along the +X direction, and this is a simple scalar integral. From Coulomb’s Law in vector form,

                                                                               \begin{array}{c}{\overline{d E}=\frac{1}{4 \pi \varepsilon_{0}} \frac{d q}{r^{2}} \hat{r}} \\ \\ {\text { whose magnitude is }} \\ \\ {\qquad d E=\frac{1}{4 \pi \varepsilon_{0}} \frac{d q}{\left(R^{2}+x^{2}\right)}}\end{array}

                                                           \begin{array}{l}{\text { The } X \text { -component is }} \\ \\ {\qquad \begin{aligned} d E_{x} &=\frac{1}{4 \pi \varepsilon_{0}} \frac{d q}{\left(R^{2}+x^{2}\right)}(\cos \theta) \\ \\ &=\frac{1}{4 \pi \varepsilon_{0}} \frac{d q}{\left(R^{2}+x^{2}\right)}\left(\frac{x}{\sqrt{R^{2}+x^{2}}}\right) \\ \\ E_{x} &=\int d E_{x}=\int \frac{1}{4 \pi \varepsilon_{0}} \frac{x d q}{\left(x^{2}+R^{2}\right)^{3 / 2}} \end{aligned}}\end{array}

As we integrate around the ring, all the terms remain constant

 Also,          \int dq = Q

                                                                        \begin{array}{l}{\text { So the total field }\left(E_{x}\right) \text { is }} \\ \\ {\qquad=\frac{1}{4 \pi \varepsilon_{0}} \frac{x}{\left(x^{2}+R^{2}\right)^{3 / 2}} \int d q} \\ \\ {=\left(\frac{1}{4 \pi \varepsilon_{0}}\right) \frac{x Q}{\left(x^{2}+R^{2}\right)^{3 / 2}}}\end{array}

So, the Net electric field is - 

 

                                                               E_{net} =\left(\frac{1}{4 \pi \varepsilon_{0}}\right) \frac{x Q}{\left(x^{2}+R^{2}\right)^{3 / 2}}

Graph  between E and X - 

                                                                   

                                                                                           If,   x= \pm \frac{R}{\sqrt{2}}

                                                                                         E_{max}=\frac{Q}{6\sqrt{3}\pi \varepsilon _{0}R^{2}}  ,

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Electric field on the axis of a charged ring

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