Suppose you are told that the linear size of everything in the universe has been doubled overnight. Can you test this statement by measuring sizes with a metre stick? Can you test it by using the fact that the speed of light is a universal constant and has not changed? What wll happen if all the clocks in the universe also start running at half the speed?

To check the pH of tap water and compare it with pH of the water in the local water body. Apparatus : Test tubes or beaker Materials : Universal pH indicator / litmus paper Procedure : implies Take water sample from tap of your home in a test tube. implies Add few drops of the universal indicator into the test tube containing tap water. implies Observe the water sample in the test tube for colour change. implies Test pH using a litmus paper, in the water sample placed in a beaker. implies Dip the litmus paper into the water in the local water body. implies Observe colour changes of the litmus paper. Observation : implies Test tube containing tap water, turns yellow colour with addition of pH indicator. implies Litmus paper does not show colour change with tap water. implies Water sample collected from pond shows red colour with pH indicator. Litmus paper turns red as it is dipped in water of local water body. Conclusion : The uncontaminated tap water is neutral while water of local water body is acidic. Can you say whether the water is polluted or not on the basis of your observations?

It is a common observation that rain clouds can be at about a kilometer altitude above the ground. (a) If a rain drop falls from such a height freely under gravity, what will be its speed? Also calculate in km/h (g = 10 m//s^(2) ). (b) A typical rain drop is about 4 mm diameter. Momentum is mass x speed in magnitude. Estimate its momentum when it hits ground. (c) Estimate the time required to flatten the drop. (d) Rate of change of momentum is force. Estimate how much force such a drop would exert on you. (e) Estimate the order of magnitude force on umbrella. Typical lateral separation between two rain drops is 5 cm. (Assume that umbrella is circular and has a diameter of 1 m and cloth is not pierced through.)