Why does it take some time to see objects in a dim room when we enter the room from bright sunlight outside?

The far point of a myopic person is $150 \ cm$ in front of the eye. Calculate the focal length and the power of a lens required to enable him to see distant objects clearly.

$A$ prism $ABC$ (with $BC$ as base) is placed in different orientations. $A$ narrow beam of white light is incident on the prism as shown in the figure. In which of the following cases,after dispersion,the third colour from the top corresponds to the colour of the sky?

Explain the structure and functioning of the human eye. How are we able to see nearby as well as distant objects?

To correct astigmatism,we use a cylindrical lens.

$A$ student finds the writing on the blackboard blurred and unclear while sitting on the last desk in a classroom. He,however,sees it clearly while sitting on the front desk at about $2\, m$ from the blackboard.
$(a)$ Draw ray diagrams to illustrate the formation of image of the blackboard writing by his eye lens when he is seated at the $(i)$ last desk,$(ii)$ front desk.
$(b)$ Name the defect of the eye from which the student is suffering.
$(c)$ Name the kind of lens that would help him to see clearly even when he is seated at the last desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.