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Two charges +q and −q are placed at distance 2a. The electric potential V at a point on the axis at distance r from the centre (r ≫ a) is approximately
AZero everywhere
BInversely proportional to r⁴
C±(1/4πε₀) · (p/r²) with positive sign on +q side
D(1/4πε₀) · (p · cosθ / r) where θ is the angle with the dipole axis
Answer & Solution
Correct answer: C. ±(1/4πε₀) · (p/r²) with positive sign on +q side
For r ≫ a, V on the axis = ±(1/4πε₀)(p/r²), with the positive sign on the +q side (θ = 0) and negative on the −q side (θ = π). General formula V = (1/4πε₀)·p·cosθ/r² gives this as a special case.
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