MP Board · Class 12 · Physics · Electric Charges and FieldsDefine electric dipole moment. State its SI unit, direction, and write its physical significance.

Electric Dipole Moment

Definition: An electric dipole consists of two equal and opposite point charges separated by a small distance ($2a$). Electric dipole moment ($\vec{p}$) is defined as the vector product of the magnitude of either charge ($q$) and the distance vector ($2\vec{a}$) separating the two charges. $$\vec{p} = q \times 2\vec{a}$$

• SI Unit: The SI unit of electric dipole moment is Coulomb-metre ($\text{C}\cdot\text{m}$).
• Direction: The electric dipole moment is a vector quantity. Its direction is conventionally taken along the dipole axis, directed from the negative charge ($-q$) to the positive charge ($+q$).

Physical Significance:

1. Behavior of Molecules: It helps in categorizing molecules into polar (e.g., $\text{H}_2\text{O}$, $\text{HCl}$) and non-polar (e.g., $\text{O}_2$, $\text{CO}_2$) based on whether they possess a permanent dipole moment.
2. Interaction with Field: It determines the magnitude of torque experienced by a system when placed in an external uniform electric field, as well as the potential energy stored in the dipole configuration.