Which lens is used to correct the defect of hypermetropia (farsightedness)?

What is meant by the spectrum of white light?

Describe an experiment to discuss the recombination of dispersed light.

$A$ person cannot see distinctly objects kept beyond $2\, m$. This defect can be corrected by using a lens of power ........ $D$.

$(i)$ Write the range of distance for a person having normal vision.
$(ii)$ $A$ person needs to use glasses for reading a newspaper. Identify the defect in his vision and the type of lens he would need to correct it.
$(iii)$ Sometimes when we enter into a dark room from bright sunlight,we are unable to see objects clearly. Why?

What are the colors obtained by mixing primary colors called?