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

Define dispersion of white light and name the colours of white light in order.

$(a)$ 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.

What is a prism?

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

The figure below shows the refraction of a ray through a prism. Copy the diagram and,ignoring dispersion at the faces $AB$ and $AC$,mark the following angles: $(i)$ The angle of incidence,$(ii)$ the angle of refraction at the face $AB$,$(iii)$ the angle of emergence,and $(iv)$ the angle of deviation.