Two point dipoles of dipole moment p₁ and p₂ are at a distance x from each other and p₁ ∥ p₂. The force between the dipoles is: (a) (1)/(4πε₀)(4p₁p₂)/(x⁴) (b) (1)/(4πε₀)(3p₁p₂)/(x³) (c) (1)/(4πε₀)(6p₁p₂)/(x⁴) (d) (1)/(4πε₀)(8p₁p₂)/(x⁴)

Answer: (c). Coaxial dipoles: field of p₁ on its axis E = (2kp₁)/(x³). Force on p₂: F = p₂|dE/dx| = p₂·(6kp₁)/(x⁴) F = (1)/(4πε₀)(6p₁p₂)/(x⁴) So the answer is (c).

Two point dipoles of dipole moment p₁ and p₂ are at a distance x from… | JEE Main 2013 (9 Apr, Shift 1)

Q72JEE Main 2013 · 9 APR · SHIFT 1Medium

Electric Dipole

Two point dipoles of dipole moment $\vec{p}_1$ and $\vec{p}_2$ are at a distance x from each other and $\vec{p}_1 \parallel \vec{p}_2$ . The force between the dipoles is:

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Answer: (c)

Coaxial dipoles: field of $p_1$ on its axis $E = \frac{2kp_1}{x^3}$ .
Force on $p_2$ : $F = p_2\left|\frac{dE}{dx}\right| = p_2\cdot\frac{6kp_1}{x^4}$
$F = \frac{1}{4\pi\epsilon_0}\frac{6p_1p_2}{x^4}$
So the answer is (c).

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Electric Dipole question from JEE Main 2013 (9 Apr, Shift 1)

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