Question

When a ray of light of frequency $6\times {10}^{14}Hz$ travels from water of refractive index $4/3$ to glass of refractive index $8/5$, its :

• A. frequency decreases by a factors of $\frac{5}{6}$
• B. speed decreases by a factor of $\frac{5}{6}$
• C. wavelength increases by a factor of $\frac{6}{5}$
• D. Speed decreases by a factor of $\frac{6}{5}$

Answer 1

The correct option is D Speed decreases by a factor of $\frac{6}{5}$

Frequency of light source will not be change because frequency depends upon the light source.

& we know that

$v_g\to$ speed in glass

$v_w\to$ speed in water

$\frac{{\mu }_w}{{\mu }_g}=\frac{v_g}{v_w}$

$v_g=\frac{{\mu }_w}{{\mu }_g}\times v_w$

$=\frac{4/3}{8/5}\times v_w=\frac{4\times 5}{3\times 8}\times v_w$

$\frac{v_g}{v_w}=\frac{5}{6}$

speed decreases by a factor of $5/6$