With the help of a ray diagram,show the formation of an image by a convex lens when the object is placed between $F$ and $2F$. Write two characteristics of the image so formed.

Multiple images are formed by a thick plane mirror. Which of the following is the brightest of all the images?

$A$ 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.

Where is the image formed when an object is placed anywhere in front of a concave lens?

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

Refractive indices of kerosene,turpentine,and water are $1.44$,$1.47$,and $1.33$ respectively. Through which of these media does light travel the fastest? Why?