Question

Light is incident on a glass block as shown in Fig. If ${\theta }_1$ is increased slightly, what happens to ${\theta }_2$?

• A. ${\theta }_2$ is unchanged
• B. ${\theta }_2$ decreases slightly
• C. ${\theta }_2$ changes abruptly, since the ray experience total internal reflection
• D. ${\theta }_2$ also increases slightly

Answer 1

Answer: (B)

if ${\theta }_1$ and ${\theta }_2$ are angle of incidence and angle of refraction respectively for a interface then according to snell's law ,
${\mu }_{1}sin{\theta }_1={\mu }_{2}sin{\theta }_2$
i.e, $sin{\theta }_1\propto sin{\theta }_2$
${\theta }_1\propto {\theta }_2$
as the ${\theta }_1$ increases the refracting angle at 1st interface increases this results in decrease of incident angle on 2nd interface which in turn decreases the refreacting angle at 2nd interface i.e, ${\theta }_2$ decreases