JEE Mains · Physics · STD 12 - Electric charges and fields
- JEE Mains 2026
- Hard
- MCQ
Two short electric dipoles \(A\) and \(B\) having dipole moment \(p_1\) and \(p_2\) respectively are placed with their axis mutually perpendicular as shown in the figure. The resultant electric field at a point \(x\) is making an angle of \(60°\) with the line joining points \(O\) and \(x\). The ratio of the dipole moments \(p_2/p_1\) is _______.

Pick an option to check your answer.
Answer & Solution
Correct Answer
(B) \(2\sqrt{3}\)
Step-by-step Solution
Detailed explanation
Let the distance of point \(x\) from the origin \(O\) be \(r\).
Point \(x\) lies on the axial line of dipole A. The electric field at \(x\) due to dipole A is directed along the horizontal axis and its magnitude is given by:
\(E_A = \dfrac{1}{4\pi\epsilon_0} \dfrac{2p_1}{r^3}\)
Point \(x\) lies on the equatorial line of dipole B. The electric field at \(x\) due to dipole B is directed perpendicular to the horizontal axis and its magnitude is given by:
\(E_B = \dfrac{1}{4\pi\epsilon_0} \dfrac{p_2}{r^3}\)
The resultant electric field makes an angle of \(60^{\circ}\) with the line \(Ox\) (the horizontal axis). Therefore, the tangent of this angle is the ratio of the perpendicular component of the electric field to the parallel component:
\(\tan 60^{\circ} = \dfrac{E_B}{E_A}\)
Substituting the expressions for \(E_A\) and \(E_B\):
\(\sqrt{3} = \dfrac{\dfrac{1}{4\pi\epsilon_0} \dfrac{p_2}{r^3}}{\dfrac{1}{4\pi\epsilon_0} \dfrac{2p_1}{r^3}}\)
\(\sqrt{3} = \dfrac{p_2}{2p_1}\)
\(\dfrac{p_2}{p_1} = 2\sqrt{3}\)
Answer: \(2\sqrt{3}\)
Point \(x\) lies on the axial line of dipole A. The electric field at \(x\) due to dipole A is directed along the horizontal axis and its magnitude is given by:
\(E_A = \dfrac{1}{4\pi\epsilon_0} \dfrac{2p_1}{r^3}\)
Point \(x\) lies on the equatorial line of dipole B. The electric field at \(x\) due to dipole B is directed perpendicular to the horizontal axis and its magnitude is given by:
\(E_B = \dfrac{1}{4\pi\epsilon_0} \dfrac{p_2}{r^3}\)
The resultant electric field makes an angle of \(60^{\circ}\) with the line \(Ox\) (the horizontal axis). Therefore, the tangent of this angle is the ratio of the perpendicular component of the electric field to the parallel component:
\(\tan 60^{\circ} = \dfrac{E_B}{E_A}\)
Substituting the expressions for \(E_A\) and \(E_B\):
\(\sqrt{3} = \dfrac{\dfrac{1}{4\pi\epsilon_0} \dfrac{p_2}{r^3}}{\dfrac{1}{4\pi\epsilon_0} \dfrac{2p_1}{r^3}}\)
\(\sqrt{3} = \dfrac{p_2}{2p_1}\)
\(\dfrac{p_2}{p_1} = 2\sqrt{3}\)
Answer: \(2\sqrt{3}\)
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