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If c denotes the speed of electromagnetic waves in free space, what is their speed in a material having dielectric constant K and relative permeability μᵣ?

1. v = 1/√(μᵣK)
2. v = c√(μᵣK)
3. v = c/√(μᵣK)
4. v = K/√(μᵣc)

Correct answer: v = c/√(μᵣK)

Solution

In a medium the wave speed is v = 1/sqrt(mu*e) = c/sqrt(mu_r*K), where K is the dielectric constant (relative permittivity) and mu_r the relative permeability.

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