Question

A thin prism $P_1$ of angle 4${}^{\circ }$ and 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 $P_2$ is :

• A. 4${}^{\circ }$
• B. 5.33${}^{\circ }$
• C. 2.6${}^{\circ }$
• D. 3${}^{\circ }$

Answer 1

The correct option is D 3${}^{\circ }$

Deviation by a thin prism

$d=A(n-1)$

For dispersion without deviation

$A(n-1)=A^{\prime }(n^{\prime }-1)$

$4(1.54-1)=A^{\prime }(1.72-1)$

$Thus{A}^{\prime }=4\times 0.54/0.72=3$