Question

Relative permeability and relative permitivity of a medium are respectively $4$ and $9$. If the magnetic induction field of the electromagnetic wave travelling in the medium is $4.2\times {10}^{-8}T$, then the magnitude of its electric field is

• A. $4.2V{m}^{-1}$
• B. $2.1\times {10}^{-8}V{m}^{-1}$
• C. $4.2\times {10}^{-8}V{m}^{-1}$
• D. $2.1V{m}^{-1}$

Answer 1

The correct option is A $4.2V{m}^{-1}$

The speed of light in the medium, $v=\frac{c}{\sqrt{{\mu }_r{ϵ}_r}}$ $=0.5\times \frac{3\times {10}^{8}m/s}{\sqrt{\left(4\right)\left(9\right)}}$ $={10}^{8}m/s$

Hence, the magnitude of electric field $=vB=0.5\times {10}^{8}m/s\times 4.2\times {10}^{-8}T$ $=2.1V{m}^{-1}$