Question

A ray of light having wavelength $720nm$ enters in a glass of refractive index $1.5$. The wavelength of the ray within the glass will be

• A. 720 nm
• B. 360 nm
• C. 1080 nm
• D. 480 nm.

Answer 1

Answer: (D)

Given: Wavelength $({\lambda }_0)=720nm$ and refractive index $(\mu )=1.5$ Since the velocity of light in a medium is given by $C=n\lambda$ and n remaining same for different media we have,
$n=\frac{c}{\lambda }=\frac{c^{\prime }}{{\lambda }^{\prime }}$
$\therefore {\lambda }^{\prime }=\frac{c^{\prime }\lambda }{c}$
Again $c^{\prime }=\frac{c}{\mu }$
Hence ${\lambda }^{\prime }=\frac{\lambda }{\mu }$
$c$ = speed is vacuum
$c^{\prime }$ = speed in medium
$\mu$ = refractive index of the medium
Therefore, wavelength of the ray in glass
$(\lambda )=\frac{{\lambda }_0}{\mu }=\frac{720}{1\cdot 5}=480nm$