# Electromagnetism - Coulomb's Law

Source:  Electromagnetism - Coulomb's Law    Tag:  inverse square law radiation
The exponent in Coulomb’s inverse square law has been found to differ from two by less than one part in a billion by measuring which of the following?

A. The charge on an oil drop in the Millikan experiment
B. The deflection of an electron beam in an electric field
C. The neutrality of charge of an atom
D. The electric force between two charged objects
E. The electric field inside a charged conducting shell
(GR8677 #86)
Solution:

The Coulomb force can be expressed by $F=&space;\frac{kq_1&space;q_2}{r^{2+n}}$.

The smallest value for n = (2.7 ± 3.1) × 10 −16 has been obtained by Williams, Faller, and Hill experiment (Phys. Rev. Lett. 26, 721, 1971).

The experiment was done by measuring the electric field inside a charged conducting shell.

See: Improved result for the accuracy of Coulombs law: A Review of the Williams, Faller, and Hill experiment.