Presbyopia is a type of far-sightedness.

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

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.

Pigments are mixed by the $......$ method to produce various colors.

$(a)$ What is "power of accommodation of the eye"?
$(b)$ What happens to the image distance when the object being viewed is moved away from the eye?

$(a)$ What is dispersion of white light? What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism.
$(b)$ $A$ glass prism is able to produce a spectrum when white light passes through it,but a glass slab does not produce any spectrum. Explain why this is so.