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?

Define absolute refractive index. Absolute refractive indices of medium $A$ and medium $B$ are $n_{a}$ and $n_{b}$ respectively. What is the refractive index of medium $B$ with respect to medium $A$? How does the velocity of light vary with change in the optical density of the media?

The magnification equation is a relation between image distance and object distance.

The focal length of a concave mirror is $30 \, cm$. Find the position of the object in front of the mirror so that the image is three times the size of the object.

When an object is placed between the principal focus $(F)$ and the pole $(P)$ of a concave mirror,what kind of image is formed?

The magnification of a real image formed by a concave mirror is always ...