For large magnifying power of a telescope

A ray of light is incident of the surface of a glass plate at an angle of incidence equal to Brewster's angle $\Phi$. If $\mu$ denotes the refractive index of glass w.r.t. air, then what will be the angle between reflected and refracted rays?

Two polaroid A and B placed in such a way that the pass-axis of polaroid are perpendicular to each other. Now, another polaroid C is placed between A and B bisecting angle between them. If intensity of unpolarised light is $I_0$ then intensity of transmitted light after passing through polaroid B will be

In a Young's double slit experiment, the intensities at two points, for the path difference $\dfrac{\lambda}{4}$ and $\dfrac{\lambda}{3}$ ($\lambda$ being the wavelength of light used) are $I_1$ and $I_2$ respectively. If $I_0$ denotes the intensity produced by each one of the individual slits, then $\dfrac{I_1 + I_2}{I_0} = $
$\left(\cos 45^\circ = \dfrac{1}{\sqrt{2}}, \cos 60 = \dfrac{1}{2}\right)$