Question

A thin prism $P_1$ with angle $6^o$ and made from glass of refractive index 1.54 is combined with another thin prism $P_2$ of refractive index 1.72 to produce dispersion without deviation. The angle of prism $P_2$ will be.

• A. $4^o{30}^{\prime }$
• B. ${8.5}^o$
• C. ${6.5}^o$
• D. None of these

Answer 1

The correct option is A $4^o{30}^{\prime }$

We know that for small angle of prism, deviation ,$\delta =A(\mu -1)$

where $A$=angle of prism

Here, net deviaton$A_1({\mu }_1-1)-A_2({\mu }_2-1)=0$

$⟹A_2=\frac{A_1({\mu }_1-1)}{{\mu }_2-1}$

$⟹A_2=\frac{6\times 0.54}{0.72}={4.5}^o$

$⟹A_2=4^o{30}^{\prime }$

Answer-(A)