First slide
Electric dipole
Question

A neutral water molecule (H20) in its vapour state has an electric dipole moment of magnitude 6.4 × 10-30 C-m. How far apart are the molecules' centres of positive and
negative charge?

Moderate
Solution

There are 10 electrons and 10 protons in a neutral water molecule.
So, its dipole moment is
p = q (21) = 10 e (21)
Hence, length of the dipole, i.e., distance between centres of positive and negative charges is

2l=p10e=6.4×10-3010×1.6×10-19=4×10-12 m=4pm

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