Where should an object be placed in front of a convex lens to obtain an image on the same side as the object?

Which mirror is used by dentists?

$A$ point object emits rays in all directions. Consider a ray emitted from the object that is parallel to the principal axis of the mirror. One of the points required to trace the reflected ray is the point of incidence itself,as shown in the figure. Select a point from the given figure through which the reflected ray passes.

The refractive index of water with respect to air is $\frac{4}{3}$ and the refractive index of glass with respect to air is $\frac{3}{2}$. What is the refractive index of glass with respect to water?

$A$ convex lens forms a real and inverted image of a needle at a distance of $50\, cm$ from the lens. Where should the needle be placed in front of the convex lens so that this image is of the same size as the object? Also, find the power of the lens.

What is the mirror formula for a spherical mirror?