Which amongst the given radiation is preferred for taking photographs in fog?
A. Ordinary visible light

B. Infrared

C. Microwave

D. X-rays

(a) A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.

(b) Why do stars twinkle? Explain.

OR

(a) Write the function of each of the following parts of human eye:

(i) Cornea (ii) Iris (iii) Crystalline lens (iv) Ciliary muscles

(b) Why does the sun appear reddish early in the morning? Will this phenomenon be observed by an astronaut on the Moon? Give reason to justify your answer.

Which phenomenon is responsible for making the path of light visible?

Give an example of a phenomenon where tyndall effect can be observed.

What is the colour of the clear sky during daytime? Give reason for it.

With the help of scattering of light, explain the reason for the difference in colours of the sun as it appears during sunrise/sunset and noon.

In an experiment to study the scattering of light by passing a beam of white light through a colloidal solution of sulphur in a transparent glass tank :

(a) Which colour is observed from the front of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?

(b) Which colour is observed from the sides of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?

Complete the following statements:

When the sun is setting, the light from it has to travel a ...............thickness of the earth's atmosphere and only ........... wavelength ........... light is able to reach us. Sunset is therefore .......

How does refraction take place in the atmosphere? Why do stars twinkle but not the planets?

Explain the phenomenon of dispersion of white light through a glass prism, using suitable ray diagram.

How can we explain the reddish appearance of sun at sunrise or sunset? Why does it not appear red at noon?