Question

A ray of light having wavelength $720\, nm$ 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 $(\lambda_{0} ) = 720 \,nm$ 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'}{\lambda'}$
$\therefore \,\lambda' = \frac{c'\lambda}{c}$
Again $c' = \frac{c}{\mu}$
Hence $\lambda' = \frac{\lambda}{\mu}$
$ c$ = speed is vacuum
$c'$ = speed in medium
$ \mu$ = refractive index of the medium
Therefore, wavelength of the ray in glass
$(\lambda)=\frac{\lambda_{0}}{\mu}=\frac{720}{1 \cdot 5}=480\, nm$