Question

A light wave is incident normally on a glass slab of refractive index $\mathrm{1.5.}$ If $4\%$ of light gets reflected and the amplitude of the electric field of the incident light is $30{\text{Vm}}^{-1}$ then the amplitude of the electric field for the wave propagating in the glass medium will be :

• A. $6{\text{Vm}}^{-1}$
• B. $24{\text{Vm}}^{-1}$
• C. $10{\text{Vm}}^{-1}$
• D. $30{\text{Vm}}^{-1}$

Answer 1

The correct option is B $24{\text{Vm}}^{-1}$

As $4\%$ of light gets reflected, so only $(100-4=96\%)$ of light comes after refraction so, the power of refracted light with respect to incident light is,

$P_{\text{refracted}}=\frac{96}{100}{P}_I$

$\Rightarrow r_2{A}_t^2=\frac{96}{100}{r}_1{A}_i^2$

$\Rightarrow A_t^2=\frac{96}{100}\times \frac{1}{\frac{3}{2}}\times (30{)}^2$

$A_t=\sqrt{\frac{64}{100}\times (30{)}^2}=\frac{8}{10}\times 30=24{\text{Vm}}^{-1}$