James Clerk Maxwell and the Second Great Unification in Physics

James Clerk Maxwell

Newton unified physics and astronomy: this was the first great unification in physics. Maxwell unified electricity and magnetism – the second great unification.  James Clerk Maxwell should be as well known as Newton. Newton has his three laws. Maxwell has four equations. We can understand Newton’s laws at high school, but we have to wait until we have studied enough mathematics to understand Maxwell’s equations. That’s why he is not well known – it looks like code.

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Maxwell’s equations

But even without the maths, we can understand what the equations mean.

What do Maxwell’s equations show us?

The first equation shows that electric fields emerge from positive charges and vanish into negative charges.

The second equation shows us that magnetic fields always form loops: they do not have a beginning or an end.

The third equation shows us that a changing magnetic field will cause an electric field. A practical example is when a wire is moved in a magnetic field, a voltage is induced.

The final equation shows us several phenomena. First, if the current is constant (e.g. in a simple circuit), you get a magnetic field (e.g. an electromagnet). But if there are no charges, a changing magnetic field will produce a changing electric field, which produces a changing magnetic field, which produces a changing electric field, and so on… In other words, an electromagnetic wave – a light wave! Maxwell discovered that light is an electromagnetic wave. More than that, this equation lets you calculate the speed that light travels in different materials.

Maxwell’s contribution to physics is huge and he deserves to be taught and remembered alongside the greats.

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