Question

When monochromatic light is refracted from a medium of refractive index $1.72$ into a vacuum, its wavelength :

• A. increases by $72$%
• B. decreases by $72$%
• C. increases by $28$%
• D. decreases by $28$%

Answer 1

Answer: (A)

increases by $72$%

We have
$\frac{{\lambda }_o-\lambda }{\lambda }=\frac{{\lambda }_o}{\lambda }-1$
We have $\frac{{\lambda }_o}{\lambda }=\mu$, where $\mu =1.72$ is the refractive index.
$⟹1.72-1=0.72=\frac{{\lambda }_o-\lambda }{\lambda }$
Hence the wavelength increases by $72$ %