When a plane mirror is rotated through a certain angle,the reflected ray turns through twice as much and the size of the image

What is meant by power of a lens? Define its $SI$ unit. You have two lenses $A$ and $B$ of focal lengths $+10\, cm$ and $-10\, cm$ respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed $8\, cm$ from the lens? Draw a ray diagram to justify your answer.

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?

Which of the following can make a parallel beam of light when light from a point source is incident on it?

Which of the following always form a virtual image?

An object $3 \, cm$ high is placed at a distance of $20 \, cm$ in front of a convex lens of focal length $12 \, cm$. Find the position,nature,and size of the image formed.