One of the basic laws of electricity is that like charges repel- positives repel positives and negative charges repel negatives.

But life is sometimes a bit more complicated and the laws, while true, need to be applied correctly.

From the ABC:

Maths shows balls with like charge attract

Contrary to what most people think, two positively-charged metal spheres that get close enough will almost always attract, according to a New Zealand physicist.

Professor John Lekner of Victoria University of Wellington describes his mathematical proof today in Proceedings of the Royal Society A.

"It's very ingrained in us that like charges repel and so how could this possibly happen?" says Lekner.

"Some colleagues and referees accepted it immediately and others were very resistant to the idea."

While most people learn in school that opposite charges attract and like charges repel, Lekner says when it comes to metal spheres, like charges don't always repel.

He developed a model that describes what happens when two positively-charged conducting spheres are placed at various distances between them.

"If they get close together they can attract even though both have a net positive charge," says Lekner.

"You get this effect when the spacing between the spheres is small relative to size of the spheres."
Mobile electrons

Lekner says because electrons are completely mobile in a conducting sphere, they are able to move to create negative and positive poles on the spheres.

The positive pole of one sphere can then attract the negative pole of the other.

Lekner says the same effect is likely to occur in conductors of different shapes but he chose spheres because the effect can be described by a relatively simple mathematical formula.

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