Monochromatic light of wavelength ${\lambda }_1$ travelling in medium of refractive index n₁ enters a denser medium of refractive index n₂. The wavelength in the second medium is

• A

  ${\mathrm{\lambda }}_1\left(\frac{{\mathrm{n}}_1}{{\mathrm{n}}_2}\right)$

• B

  ${\mathrm{\lambda }}_1\left(\frac{{\mathrm{n}}_2}{{\mathrm{n}}_1}\right)$

• C

  ${\lambda }_1$

• D

  ${\mathrm{\lambda }}_1\left(\frac{{\mathrm{n}}_2-{\mathrm{n}}_1}{{\mathrm{n}}_1}\right)$