Question

Three prisms of crown glass, each have angle of prism $9^{\circ }$ and two prisms of flint glass are used to make direct vision spectroscope. What will be the angle of flint glass prisms if $\mu$ for flint is $1.60$ and $\mu$ for crown glass is $1.53$.

• A. ${11.9}^{\circ }$
• B. ${16.0}^{\circ }$
• C. ${15.3}^{\circ }$
• D. ${9.11}^{\circ }$

Answer 1

The correct option is A ${11.9}^{\circ }$

Crown glass, each have angle of prism$=90°$

Two prisms of fint glass are used to make direct vision spectroscope

$\mu =1.60$

Hence total deviation$=0$

${\delta }_1+{\delta }_2+{\delta }_3+{\delta }_4+{\delta }_5=({\mu }_1-1)A_1-({\mu }_2-1)A_2+({\mu }_3-1)A_3-({\mu }_4-1)A_4-1({\mu }_5-1)A_5=0\Rightarrow 2\times A_2(1.6-1)=3(1.53-1)\times 9A_2=3\left(\frac{53\times 9}{1.2}\right)=11.9°$