What happens when a light ray incident normally on the surface of a glass slab enters from air into the glass?

You have a spherical mirror. The image of an object placed in front of the mirror is virtual. If the position of the object is changed,the image remains virtual and erect. Is the spherical mirror concave or convex?

Draw ray diagrams showing the image formation by a concave lens when an object is placed:
$(a)$ at the focus of the lens
$(b)$ between focus and twice the focal length of the lens
$(c)$ beyond twice the focal length of the lens

Multiple images are formed by a thick plane mirror. Which of the following is the brightest of all the images?

$A$ ray of light is incident obliquely on a glass slab. Draw a ray diagram showing the path of the light ray. Clearly,mark the angle of incidence,angle of refraction,angle of emergence,and lateral displacement of the ray. Give a formula to find the refractive index of the glass slab in terms of the angle of incidence and the angle of refraction.

Beams of light are incident through the holes $A$ and $B$ and emerge out of the box through the holes $C$ and $D$ respectively,as shown in the figure. Which of the following could be inside the box?