Which scientist established that white light is composed of seven constituent colors?

An old person is unable to see clearly nearby objects as well as distant objects. $(i)$ What defect of vision is he suffering from? $(ii)$ What kind of lens will be required to see clearly the nearby as well as distant objects? Give reasons.

What is the far point of a normal human eye?

$(i)$ 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?

Give one example in nature where we can see the dispersion of white light.

In the spectrum obtained by the dispersion of white light through a prism,which color band is located in the middle?