For what position of the object does a concave mirror form a real and diminished image?

Refractive index of diamond with respect to glass is $1.6$ and absolute refractive index of glass is $1.5$. Find out the absolute refractive index of diamond.

Name two spherical mirrors. Define them. Write any three points of difference between them.

What is the focal length of a convex lens having power $+5.0 \,D$?

What does negative magnification mean in the context of spherical mirrors?

One half of a convex lens is covered with a black paper.
$(a)$ Show the formation of the image of an object placed at $2F_{1}$ of such a covered lens with the help of a ray diagram. Mention the position and nature of the image.
$(b)$ Draw the ray diagram for the same object at the same position in front of the same lens,but now uncovered. Will there be any difference in the image obtained in the two cases? Give a reason for your answer.