Question

The refractive index of flint glass is 1.65.what is the speed of light in the glass?

Answer 1

Explanation:

Speed of light in vacuum is 3×10^8 m/s

Speed in Flint glass = (3× 10^8)/1.65 m/s = 1.818 × 10^8 m/s

Answer 2

Given :

$\bf Refractive \: index \: of \: flint \: glass, \: η_{g} = 1.65$

To Find :

$\bf Speed \: of \: light \: in \: glass, v_{g}$

Solution :

$\bf We \: know \: that \: speed \: of \: light \: in \: air, c=3×10⁸m/s$

Now, by formula :

$\bf η_{g} = \dfrac{c}{v_{g}}$

$\bf \implies v_{g} = \dfrac{c}{η_{g}}$

$\bf \implies v_{g} = \dfrac{3 \times 10^{8}m/s}{1.65}$

$\bf \implies v_{g} = \dfrac{3}{1.65}\times 10^{8}m/s$

$\bf \implies v_{g} = \dfrac{3 \times 100}{165}\times 10^{8}m/s$

$\bf \implies v_{g} = \dfrac{\cancel{3} \times 100}{\times{\cancel{165}}_{55}}\times 10^{8}m/s$

$\bf \implies v_{g} = \dfrac{100}{55}\times 10^{8}m/s$

$\bf \implies v_{g} = 1.8181... \times 10^{8}m/s$

$\bf \implies v_{g} = 1.82 \times 10^{8}m/s \: (approx.)$

$\bf \therefore Speed \: of \: light \: in \: glass, v_{g} = 1.82 \times 10^{8}m/s \: (approx.)$