A thin prism $\mathrm{P}_{1}$ with angle $4^{\circ}$ and made from glass of refractive index $1 \cdot 54$ is…
A thin prism $\mathrm{P}_{1}$ with angle $4^{\circ}$ and made from glass of refractive index $1 \cdot 54$ is
combined with another thin prism $\mathrm{P}_{2}$ made from glass of refractive index $1 \cdot 72$ to
produce dispersion without deviation. The angle of prism for $\mathrm{P}_{2}$ is
$4^{\circ}$
$5 \cdot 33^{\circ}$
$2 \cdot 6^{\circ}$
$3^{\circ}$
Solution
For thin prism the angle of deviation $\delta=\mathrm{A}(\mathrm{n}-1)$
$\therefore \delta_{1}=\delta_{2} \quad$ for no deviation
$\therefore A_{1}\left(n_{1}-1\right)=A_{2}\left(n_{2}-1\right)$
$4(1.54-1)=\mathrm{A}_{2}(1.72-1)$
$\therefore 4 \times 0.54=\mathrm{A}_{2} \times 0.72$
$\mathrm{A}_{2}=\frac{4 \times 0.54}{0.72}=3^{\circ}$