Question

Critical angle of glass is ${\theta }_1$ and that of water is ${\theta }_2$. The critical angle for water and glass surface would be $({\mu }_g=3/2,{\mu }_w=4/3)$.

• A. Less than ${\theta }_2$
• B. Between ${\theta }_1$ and ${\theta }_2$
• C. Greater than ${\theta }_2$
• D. Less than ${\theta }_1$

Answer 1

Answer: (C)

Greater than ${\theta }_2$

$\sin {\theta }_1=\frac{1}{{\mu }_g}$ and $\sin {\theta }_2=\frac{1}{{\mu }_w}$
Since ${\mu }_g>{\mu }_w,{\theta }_1<{\theta }_2$
Critical angle $\theta$ between glass and water will be given by
$\sin \theta =\frac{{\mu }_w}{{\mu }_g}$
or $\theta >{\theta }_2$
Note: Critical angle increases as the relative refractive index is decreased.