Physics

Problem

An electromagnetic wave travels through a non-magnetic dielectric with relative permittivity

\varepsilon_r = 4

and

\mu_r = 1

. Its magnetic field has a peak value

B_0 = 3\times10^{-7}\,\text{T}

and its wavelength in the medium is

0.60\,\text{m}

. The peak value of its electric field

E_0

is a)

90\,\text{V\,m}^{-1}

45\,\text{V\,m}^{-1}

6.36\times10^{1}\,\text{V\,m}^{-1}

22.5\,\text{V\,m}^{-1}

Intuitive explanation

The key is understanding how the wave speed changes inside a dielectric, and then using the relationship between electric and magnetic field amplitudes in any medium. The wave speed in the medium depends on $\varepsilon_r$ , which slows the wave down and changes its wavelength—but the ratio $E_0/B_0$ is always $v$ , the speed in that medium. Find the speed from the wavelength and frequency, then use it to recover $E_0$ from the given $B_0$ .

Intuitive explanation

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