An electric dipole has a fixed dipole moment p, which makes angle θ with respect to x-axis. When subjected to an electric field E₁ = Ei, it experiences a torque T₁ =. When subjected to another electric field E₂ = √(3)E₁j it experiences a torque T₂ = -T₁. The angle θ is: (a) 90o (b) 45o (c) 30o (d) 60o

Answer: (d). p = p(cos θ i + sin θ j), τ = p × E. T₁ = p × E i = -pEsin θ k T₂ = p × √3 E j = √3 pEcos θ k T₂ = - T₁ ⇒ √3cos θ = sin θ ⇒ tan θ = √3 So the answer is (d) 60°.

An electric dipole has a fixed dipole moment p, which makes angle θ… | JEE Main 2017

Q69JEE Main 2017Medium

Electric Dipole

An electric dipole has a fixed dipole moment $\vec{p}$ , which makes angle $\theta$ with respect to x-axis. When subjected to an electric field $\vec{E}_1 = E\hat{i}$ , it experiences a torque $\vec{T}_1 = \tau\hat{k}$ . When subjected to another electric field $\vec{E}_2 = \sqrt{3}E_1\hat{j}$ it experiences a torque $\vec{T}_2 = -\vec{T}_1$ . The angle $\theta$ is:

Show answer and solution

Answer: (d)

$\vec p = p(\cos\theta\,\hat i + \sin\theta\,\hat j)$ , $\vec \tau = \vec p \times \vec E$ .
$\vec T_1 = \vec p \times E\hat i = -pE\sin\theta\,\hat k$
$\vec T_2 = \vec p \times \sqrt3 E\hat j = \sqrt3\,pE\cos\theta\,\hat k$
$\vec T_2 = -\vec T_1 \Rightarrow \sqrt3\cos\theta = \sin\theta \Rightarrow \tan\theta = \sqrt3$
So the answer is (d) $60^\circ$ .

Report a mistake

Electric Dipole question from JEE Main 2017

More questions on Electric Dipole