Which type of reflection will be represented by light reflected from a book?

State the sign convention for lenses regarding object and image distances.

With respect to air,the refractive indices of ice and rock salt are $1.31$ and $1.54$ respectively. Calculate the refractive index of rock salt with respect to ice.

State the relation between object distance,image distance,and focal length of a concave or convex mirror. $A$ concave mirror produces a two times magnified real image of an object placed at $10 \ cm$ from it. Find the position of the image.

In the case of a convex mirror,if the object is moved away from the surface of the mirror,how do the position and size of the image change?

Give the mathematical expression for the power of a lens.