Question

Beams of red, green and violet light are falling on the refracting face of a thin prism, all at same angle of incidence. If their angles of deviation are ${\theta }_1,{\theta }_2$ and ${\theta }_3$ respectively, then

• A. ${\theta }_1={\theta }_2={\theta }_3$
• B. ${\theta }_1<{\theta }_2<{\theta }_3$
• C. ${\theta }_1>{\theta }_2>{\theta }_3$
• D. ${\theta }_2>{\theta }_1>{\theta }_3$

Answer 1

The correct option is B ${\theta }_1<{\theta }_2<{\theta }_3$

For deviation to be greater, refrective index should be more or wavelength should be less.
i.e $\delta \propto \frac{1}{\lambda }$
The order of wavelength for red, green and violet light is
$\Rightarrow {\lambda }_R>{\lambda }_G>{\lambda }_V$
The order of deviation is
${\delta }_R<{\delta }_G<{\delta }_V$
Then the order of angular deviation is
${\theta }_1<{\theta }_2<{\theta }_3$