Take three bowls and mark as A,B,C . Pour lukewarm milk in bowl. A hot milk in bowl B, cold milk in bowl C. Add one tea spoon of curd or butter milk in three bowls and stir them slightly. Cover the bowls with lids. Keep the bowls undisturbed for five to six hours. In which bowl milk turned into curd? Give your reasons.

Why do we notice change in bowl 2 through we took milk in both bowls 2 and3 in curd formation?

Take half glass of water in two beakers or bowls separately. Add 5 to 10 spoons of sugar in the water, and add 2 to 3 spoons of yeast in one of the bowls. Close the bowls with lids and keep them in a warm place. After 3 to 4 hours remove the lids and smell.

A glass full of hot milk is poured on the table. It begins to cool gradually. Which of the following is correct? (a) The rate of cooling is constant till milk attains the temperature of the surrounding. (b) The temperature of milk faills off exponentially with time. ( c) While cooling, there is a flow of heat from milk to the surrounding as well as from surrounding to the milk but the net flow of heat is from milk to the surrounding and that is why it cools. (d) All three phenomenon, conduction, convection and radiation are responsible for the loss of heat from milk to the surroundings.