What is the absolute refractive index of common glass?

Draw a ray diagram showing the path of rays of light when it enters with oblique incidence: $(i)$ from air into water; $(ii)$ from water into air.

$A$ ray of light $XY$ is incident on a spherical mirror as shown in the diagram. Redraw the diagram and mark the normal,angle of incidence and angle of reflection.

For a concave mirror,if the object distance $u = \infty$,then the image distance $v = ..........$.

$(a)$ The refractive index of diamond is $2.42$. What is the meaning of this statement?
$(b)$ Redraw the diagram given below in your answer book and complete the path of the ray.
$(c)$ What is the difference between virtual images produced by concave and convex mirrors?
$(d)$ What does the negative sign in the value of magnification produced by a mirror indicate about an image?

$A$ thin lens has a focal length of $-12\, cm$. Is it a convex lens or a concave lens?