An electric dipole is placed along the $x$ -axis at the origin $O$. A point $\mathrm{P}$ is at a distance of…

An electric dipole is placed along the $x$ -axis at the origin $O$. A point $\mathrm{P}$ is at a distance of $20 \mathrm{~cm}$ from this origin such that OP makes an angle $\pi / 3$ with the $x$ -axis. If the electric field at P makes an angle $\theta$ with the $x$ -axis, the value of $\theta$ would be
  1. $\frac{\pi}{3}$
  2. $\frac{\pi}{3}+\tan ^{-1}\left(\frac{\sqrt{3}}{2}\right)$
  3. $\frac{2 \pi}{3}$
  4. $\tan ^{-1}\left(\frac{\sqrt{3}}{2}\right)$

Solution

From figure, $\theta=\frac{\pi}{3}+\alpha$, where $\tan \alpha=\frac{\mathrm{E}_{2}}{\mathrm{E}_{1}}=\left(\frac{\mathrm{p} \sin \theta}{4 \pi \epsilon_{0} \mathrm{r}^{3}}\right)\left(\frac{4 \pi \in_{0} \mathrm{r}^{3}}{2 \mathrm{p} \cos \theta}\right)=\frac{1}{2} \tan \theta$
$\tan \left(\theta-\frac{\pi}{3}\right)=\frac{1}{2} \tan \frac{\pi}{3}=\frac{\sqrt{3}}{2}$
or $\theta-\frac{\pi}{3}=\tan ^{-1}\left(\frac{\sqrt{3}}{2}\right)$
or $\alpha=\tan ^{-1}\left(\frac{\sqrt{3}}{2}\right)$
or $\theta=\frac{\pi}{3}+\tan ^{-1}\left(\frac{\sqrt{3}}{2}\right)$

Asked in: JEE Mains - Electrostatics - Test 5

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