Question

When the red light passes from air $(n=1)$ into glass $(n=1.5)$, Calculate its new wavelength?

• A. $4\times {10}^{-7}m$
• B. $4\times {10}^{-6}m$
• C. $2.5\times {10}^{-7}m$
• D. $6\times {10}^{-7}m$
• E. $9\times {10}^{-7}m$

Answer 1

The correct option is A $4\times {10}^{-7}m$

Refractive index of glass $n_g=1.5$

Refractive index of air $n_a=1$

Wavelength of red light in air ${\lambda }_a=600nm=6\times {10}^{-7}$ $m$

$\therefore$ Wavelength of red light in glass ${\lambda }_g=\frac{n_a\times {\lambda }_a}{n_g}=\frac{1\times 6\times {10}^{-7}}{1.5}=4\times {10}^{-7}$ $m$