What is the distance between the principal focus and the center of curvature of a spherical mirror?

The distance between the object kept at $2 \, m$ from a plane mirror and its image is $.....$ (in $, m$)

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between the lens and the image is $80 \, cm$,at what distance should the candle be placed from the lens? What is the nature of the image at a distance of $80 \, cm$ from the lens (in $, cm$)?

The image formed by a convex spherical mirror is always:

The ray diagram given below illustrates the experimental setup for the determination of the focal length of a converging lens using a plane mirror.
$(i)$ State the magnification of the image formed.
$(ii)$ Write two characteristics of the image formed.
$(iii)$ What is the name given to the distance between the object and the optical centre of the lens in the given diagram?

$(a)$ What is meant by refraction of light?
$(b)$ If on applying Cartesian sign convention for spherical lenses the image distance obtained is negative,state the significance of the negative sign.