Question

A beam of monochromatic blue light of wavelength $4200\mathring{A}$ in air travels in water (refractive index $=\frac{4}{3}$). Its wavelength in water will be :

• A. $2800\mathring{A}$
• B. $3150\mathring{A}$
• C. $4000\mathring{A}$
• D. $5600\mathring{A}$

Answer 1

The correct option is B $3150\mathring{A}$

Refractive index, ${}_a{\mu }_w=\frac{{\lambda }_{air}}{{\lambda }_{water}}$

$\Rightarrow \frac{4}{3}=\frac{4200}{{\lambda }_{water}}$

$\therefore {\lambda }_{water}=4200\times \frac{3}{4}$

$=3150A^o$