The distance between H+  and Cl−  ions in HCI molecule is 1.28 A∘ . What will be the potential due to this dipole at a distance of 12 A∘  on the axis of dipole?

Here, 2a=1.28  A∘=1.28  × 10−10m            V=?, r=12A∘=12  × 10−10m As the point is on axial line of dipole∴                V=k q (2 a)r2 =9  × 109×1.6  × 10−19(1.28  × 10−10)(12 × 10−10)2 =0.128 ≈ 0.13 V