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Field of a dipole
Intermediate
On the axis the field is 2kp/r³.
E = 2kp/r³On the axis far away E = 2kp/r³; on the equatorial line E = kp/r³ with opposite direction. It falls as 1/r³, faster than a point charge.
Biological molecules interact through dipole fields.
Valid for r ≫ d.
In more detail
The field of a dipole falls off as 1/r³ at large distances, faster than that of a point charge. Its direction depends on the angle from the dipole axis.
Real-world uses
- Molecular interactions are often modelled using dipole fields.
- Dipole antennas are designed around this field pattern.
- Chemists use the dipole field to explain how polar molecules affect the forces between nearby molecules.
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Frequently asked questions
Why does it fall faster?
Because the two charges partly cancel at large distances.
Is it always inverse cube?
At large distances along the dipole axis or perpendicular to it, yes.
Why does the dipole field fall off faster than a point charge?
Its two charges partly cancel at large distances, so the field decreases as the cube of the distance.
Related topics in Electrostatics
Field of a point charge · Electric field lines · Electric dipole · Torque on a dipole in a field · Potential energy of a dipole · Electric flux