Which liquid fills the space between the eye lens and the retina?

$(a)$ 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.

Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?

Which of the following colors is not a primary color?

What is meant by the least distance of distinct vision? How does this vary between the very young and old people?

$A$ convex lens can be used to correct long-sightedness (hypermetropia).