Answer
$\Delta\theta =0.4^{\circ}$
Work Step by Step
Model: Use the ray model of light
Visualize:
Using Snell’s law,
$n_{air}\ sin30^{\circ} = n_{red}\sin\theta_{red}$
$\Rightarrow \theta_{red}= sin^{-1}(\frac{sin30^{\circ}}{1.52}) = 19.2^{\circ}$
$n_{air}\ sin30^{\circ} = n_{violet} \ sin\theta_{violet}$
$\Rightarrow \theta_{violet}= sin^{-1}(\frac{sin30^{\circ}}{1.55}) = 18.8^{\circ}$
Thus the angular spread is:
$\Delta\theta=\theta_{red}-\theta_{violet} =19.2^{\circ}-18.8^{\circ}=0.4^{\circ}$
