NEET 2022 · PhysicsDipole fieldPrevious Year Question
Two point charges −q and +q are placed at a distance L apart, as shown in the figure. The magnitude of the electric field intensity at a distance R (R >> L) varies as
Answer: (B) 1/R³. Answer: (b) Solution: Two equal and opposite point charges +q and −q separated by a small distance L constitute an electric dipole of moment p = qL.
- A.1/R²
- B.1/R³✓
- C.1/R⁴
- D.1/R⁶
Correct Answer
(B) 1/R³
Solution & Explanation
Answer: (b) Solution: Two equal and opposite point charges +q and −q separated by a small distance L constitute an electric dipole of moment p = qL. The electric field of a dipole at a point far away (R >> L) is E = (1/4πε₀)·(p/R³)·√(1 + 3cos²θ), which for any fixed direction scales as E ∝ 1/R³. (Compared with a single point charge, whose field ∝ 1/R², the dipole field falls off faster because the two opposite-charge fields nearly cancel.) Hence E ∝ 1/R³.
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