# Relating electric constants to the speed of light ?

1. Dec 6, 2009

### cragar

1/sqrt(EP)=c
where E= Permittivity constant
P= permeability constant .
My teacher wanted us to think about this result that Maxwell got
and how it would lead to problems and eventually lead to relativity
can some one give me a hint what he is getting at this is not a home work problem he just wanted us to think about it .

2. Dec 7, 2009

### diazona

Well... hopefully you know that the vacuum permeability and permittivity (the electric and magnetic constants) were determined by experiments which, at the time, seemed to be completely unrelated to light. I'm talking about measuring the tiny forces between charged pith balls and electric wires with current flowing through them, that sort of thing. Then they calculated $1/\sqrt{\epsilon_0 \mu_0}$ and found that it was equal to the speed of light.

Now think about this: what if you took all those experiments on some futuristic spaceship, fired it up to half the speed of light, and did the experiments again? What would happen to the value of the electric and magnetic constants?

3. Dec 7, 2009

### cragar

thanks for the response , so like if I have charged particles and I am moving
to someone on the ground the particles are moving so we would perceive different magnetic fields .

4. Dec 7, 2009

### Born2bwire

Maxwell's addition of the displacement current that completed his equations also allowed him to derive wave equations for the electric and magnetic fields. The speed of these wave equations were found to be c. So Maxwell's equations not only predict electromagnetic waves, they also stipulate that their speed in vacuum is c.

This is the starting point for deriving special relativity.

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