Answer
(a) $72^{\circ}$
(b) No
Work Step by Step
(a) We can find the value of $\theta$ as follows:
$\theta=sin^{-1}[\frac{n_{glass}}{n_{air}}cos(sin^{-1}(\frac{n_{air}}{n_{glass}}))]$
We plug in the known values to obtain:
$\theta=sin^{-1}[\frac{1.38}{1.00}cos(sin^{-1}(\frac{1.00}{1.38}))]$
This simplifies to:
$\theta=72^{\circ}$
(b) We know that the angle of incidence at the vertical surface will be less as compared to the critical angle, if the value of $\theta$ is increased.
