Units of electric dipole moment in SI What are the correct SI units for electric dipole moment p?

Introduction / Context:
The electric dipole moment p quantifies the strength of a separated pair of equal and opposite charges. Knowing its units is fundamental in electromagnetics, molecular physics, and materials science when converting between microscopic and macroscopic descriptions.

Given Data / Assumptions:

• Definition: For two charges +q and −q separated by vector d, p = q d.
• SI base units: charge in coulombs (C) and length in metres (m).
• We are not using derived non-SI units such as Debye (common in molecular physics).

Concept / Approach:
Dimensional analysis directly follows from the definition p = q d. Multiply a charge by a distance to obtain units.

Step-by-Step Solution:
Write p = q d.Units: q → C; d → m.Therefore, units of p are C·m (coulomb–metre).Select the option that states “coulomb–metre”.

Verification / Alternative check:
Continuum polarization P has units C/m^2 and relates to p via P = dipole moment per unit volume; this is consistent because dividing C·m by m^3 yields C/m^2.

Why Other Options Are Wrong:
“coulombs” lacks distance; “coulomb/metre” and “coulomb/m^2” belong to field quantities like line or surface charge density, not dipole moment.

Common Pitfalls:
Confusing dipole moment (C·m) with polarization (C/m^2) or electric field (V/m).

Final Answer:
coulomb–metre