Write the relationship between object distance $(u)$,image distance $(v)$,and focal length $(f)$ for a spherical mirror.

$A$ girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens. State the reason for this observation.

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

Which symbol is used for the refractive index?

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?

The refractive index of dense flint glass is $1.65$ and for alcohol it is $1.36,$ with respect to air. What is the refractive index of dense flint glass with respect to alcohol?