Formula & Calculator
Electric Dipole Moment
Describes the strength and orientation of an electric dipole formed by two opposite charges.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| p | Electric dipole moment | C·m |
| q | Magnitude of charge | C |
| d | Separation distance between charges | m |
What it means
The electric dipole moment p is a measure of the separation of positive and negative charges in a system. It is defined as p = q·d, where q is the magnitude of each charge and d is the displacement vector from negative to positive charge. The dipole moment is a vector quantity and is important in understanding the behaviour of molecules, dielectrics, and antennas. In an external electric field, a dipole experiences a torque that tends to align it with the field. Dipoles play a key role in the polarisation of dielectric materials, affecting the overall capacitance of a capacitor. In electromagnetism, the dipole field is the leading term in the multipole expansion. Example: For a pair of charges +1.6×10⁻¹⁹ C and −1.6×10⁻¹⁹ C separated by 0.1 nm (1×10⁻¹⁰ m), the dipole moment is p = 1.6e-19 * 1e-10 = 1.6×10⁻²⁹ C·m. This is typical of a polar molecule like water.
Worked example
Electric Dipole Moment – Practical Example
Real‑World| Parameter | Value |
|---|---|
| q | 2 µC = 2×10⁻⁶ C |
| d | 1 cm = 0.01 m |
| Formula | p = q·d |
Common mistakes
- Charge q and separation d: The dipole moment points from negative to positive charge.
- Units: C·m (coulomb‑metre).
- Vector: It is a vector quantity – direction matters.
- Torque: A dipole in an electric field experiences torque τ = p × E.
- Potential energy: U = −p·E for a dipole in a field.
Applications
The electric dipole moment p = q·d represents the separation of opposite charges, a vector pointing from negative to positive. This concept is vital for understanding the behaviour of polar molecules, dielectric polarisation, and the generation of electromagnetic radiation. Engineers use it in designing microwave antennas, studying material polarisation, and understanding the interaction of fields with matter. By calculating the dipole moment, they can predict the response of materials to electric fields and design devices such as phase shifters and modulators. This formula is fundamental in electromagnetics and materials science.
- Design of microwave and RF components (phase shifters, antennas)
- Understanding dielectric polarisation and permittivity
- Molecular and chemical analysis via dipole moments
- Electromagnetic field interaction with materials
- Educational foundation of dipole radiation