# A light wave has wavelength $6000 A^{\circ}$ in vacuum. The wavelength of this light when it passes through a certain glass of refraction index $(\mu =1.5 )$ is

$(a)\;4000 A^{\circ} \\ (b)\;6000 A^{\circ} \\ (c)\;9000 A^{\circ} \\ (d)\;15000 A ^{\circ}$

$\large\frac{\mu _1}{\mu_2}=\frac{\lambda_2}{\lambda_1}$
$\mu_1$ - refractive index for air
$\mu_2$ - refractive index for glass
$\lambda _1$ -wave length in air
$\lambda _2$ -wave length in glass
$\frac{1}{1.5}=\frac{\lambda_2}{6000}$
$\lambda _m= 4000 A^{\circ}$
Hence a is the correct answer.