Due to atmospheric refraction of light,the Sun appears to rise $................$ its actual sunrise.

What is meant by scattering of light? Mention the factor on which it depends. Explain why the colour of the clear sky is blue? An astronaut in space finds the sky to be dark. Explain the reason for this observation.

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

$(a)$ 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.

In the human eye,the image of an object is formed on the $................$.

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