To clean their spectacles people often breathe out on glasses to make them wet.Explain why the glasses become wet.

Carry out the following osmosis experiment: Take four peeled potato halves and scoos each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.(a) Now, Keep cup A empty.(b)Put one teaspoon sugar in cup B.(c)Put one teaspoon salt in cup c.(d)put one teaspoon sugar in the boiled potato cup D.Keep these for two hours then observe the four potato cups and answer the following:Explain why water gathers in the hollowed portion of B and C.

A myopic person has been using spectacles of power -1.0D for distant vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened.

End of a glass tube becomes round on heating Explain.

Explain why The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.