Electric Dipole

What is an Electric Dipole?

An electric dipole is formed by two equal and opposite point charges, $+q$ and $-q$, separated by a fixed distance. The separation between the charges is taken as $2a$ (so the distance from the centre to each charge is $a$).

• The dipole axis is the line joining the two charges.
• By convention, the direction of the dipole is from the negative charge ($-q$) to the positive charge ($+q$).
• The centre of the dipole is the midpoint of the line joining the two charges.

Why does a dipole produce an electric field?

Even though the total charge of a dipole is zero ($q + (-q) = 0$), the electric field is not zero. This is because the two charges are separated in space. Their individual fields do not exactly cancel out — they add vectorially to produce a net field.

• At points very far from the dipole (distances $r \gg 2a$), the fields from $+q$ and $-q$ nearly cancel.
• As a result, the electric field of a dipole falls off faster than that of a single point charge.
  • For a single charge: field $\propto 1/r^2$.
  • For a dipole: field $\propto 1/r^3$ at large distances.

This faster decay is a key qualitative feature of dipole fields.

Key Takeaways

• A dipole has zero net charge but a non-zero electric field. …