Five-dimensional Kaluza-Klein theory with a source

A free test particle in five-dimensional Kaiuza Klein space-time will show its electricity in the reduced four-dimensional space-time when it moves along the fifth dimension. In the light of this observation, we study the coupling of a five-dimensional dust field with the Kaluza-Klein gravity. It turns out that the dust field can curve the five-dimensional space-time in such a way that it provides exactly the source of the electromagnetic field in the four-dimensional space-time after the dimensional reduction.