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The speed of plane electromagnetic waves is maximum in ______.

#### Options

glass

vaccum

tourmaline

water

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#### Solution

The speed of plane electromagnetic waves is maximum in **vaccum**.

**Explanation:**

`v = 1/(sqrt(mu_0 mu_tau∈_"o"∈_"r")) = "c"/sqrt(∈_"r"mu_"r")`

Since, `∈_"r"mu_"r"` > 1,

Thus, c (speed of light in vacuum) > v (speed of light in any other medium)

Hence it is maximum in a vacuum.

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