# Speed of EM waves in material

**1. The problem statement, all variables and given/known data**

An EM wave with frequency 87Mhz travels in an insulating ferromagnetic material with [itex]\mu_0 \mu_r = 1000[/itex] and [itex]\epsilon_0 \epsilon_r = 10[/itex] – What is the speed of the EM wave in the material.

**2. Relevant equations**

[itex]v=(\sqrt{\mu_0 \mu_r \epsilon_0 \epsilon_r})^{-1}[/itex]

**3. The attempt at a solution**

For part A I am really confused, well kind of, I am wondering whether in the text for part A they made a mistake and it should be just mu_r=1000 and just epsilon_r=10 , instead of the product of them and the constants sub0. Because if I do it as in the question I get a speed of 0.01m/s as shown below.

[itex]

v=\frac{1}{\sqrt{10 \times 1000}} = 0.01 m/s

[/itex]

But if I take it to be the relative values on their own I get a much higher value as shown below.

[itex]

v=\frac{1}{\sqrt{8.85\times 10^{-12} \times 1000 \times 4 \times \pi \times 10^{-7} \times 10 }} = 2.99 \times 10^6 m/s

[/itex]

So my question really, is it possible to have such slow propagating EM waves in materials like that?

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