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How does the electric field of a dipole at an axial point at distance r vary with r?

1. Directly proportional to r³
2. Inversely proportional to r³
3. Directly proportional to r²
4. Inversely proportional to r²

Correct answer: Inversely proportional to r³

Solution

For a short dipole the axial field is E = (1/(4*pi*e0)) * 2p/r³, which is inversely proportional to r³. This faster decay (compared to 1/r² for a point charge) arises because the fields of the two opposite charges nearly cancel.

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