Find the focal length of a convex lens,if its power is $+2.0 \ D$. (in $m$)

When light of two colours $A$ and $B$ is passed through a plane boundary; $A$ is bent more than $B$. Which colour travels more slowly in the second medium?

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.

Which of the lenses with focal lengths $10 \, cm$,$20 \, cm$,$25 \, cm$,and $50 \, cm$ has the maximum power (in $, cm$)?

How many times is the velocity of light in a vacuum compared to the velocity of light in water?

Where should the light source (bulb) be placed in the reflector of a searchlight or torch so that the light rays travel over a long distance?