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## Homework Statement

I'm trying to understand an approximation Griffiths does (in his solutions' manual - exercise 9.18-b) and I'm not quite getting it.

Let

$$k = \omega \sqrt{\dfrac{\epsilon \mu}{2}} [\sqrt{ 1 + (\dfrac{\sigma}{\epsilon \omega}})^2-1]^{1/2}$$

He says that, because ##\sigma >> \omega \epsilon##, we have:$$k = \sqrt{\dfrac {\mu \sigma \omega}{2}}$$

## The Attempt at a Solution

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Essentially, my attempt was to say that ##(\dfrac{\sigma}{\epsilon \omega})^2 \approx \sigma ^2##. After that, and since sigma >> 1, I'd say that ##\sqrt {1 + \sigma ^2} \approx \sigma##, and for the same reasoning ##\sigma -1 \approx \sigma##, which would make everything inside the straight brakets be ##\sqrt{\sigma}##. After all this, ##k## would be ##\omega \sqrt {\dfrac{\epsilon \mu \sigma}{2}}##. Now, sadly, that's no way near the solution I'm supposed to arrive.

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