Question

The angle of crown glass $(\mu =1.52)$ prism is $5^o$. What should be the angle of flint glass $(\mu =1.63)$ prism so that the two prisms together may be used in a direct vision spectroscope?

• A. $-{2.14}^o$
• B. $+{2.14}^o$
• C. $-{4.12}^o$
• D. $+{4.12}^o$

Answer 1

Answer: (C)

$-{4.12}^o$

For direct vision spectroscope,
${\delta }_1+{\delta }_2=0$

$\therefore ({\mu }_1-1)A_1+({\mu }_2-1)A_2=0$

$\Rightarrow A_2=-\left[\frac{{\mu }_1-1}{{\mu }_2-1}\right]A_1$ $=-\left[\frac{1.52-1}{1.63-1}\right]\times 5^0=-{4.12}^o$