Question

When the angle of incidence is ${60}^o$ on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

• A. $\sqrt{2}\times {10}^{8}m{s}^{-1}$
• B. $\sqrt{3}\times {10}^{8}m{s}^{-1}$
• C. $2\times {10}^{8}m{s}^{-1}$
• D. $3\times {10}^{8}m{s}^{-1}$

Answer 1

Answer: (B)

$\sqrt{3}\times {10}^{8}m{s}^{-1}$

Refractive index of glass

${\mu }_g=tan\left({\theta }_p\right)$

where, ${\theta }_p$ polarising angle

${\mu }_g=tan{60}^o=\sqrt{3}$

$m{u}_g=\frac{c}{v_g}$

$\frac{c}{v_g}=\sqrt{3}$

$v_g=\frac{3\times {10}^8}{\sqrt{3}}=\sqrt{3}\times {10}^{8}m/s$