Take 6-7 glass cups. Arrange them in a line and fill them with water gradually increasing water level from one end to other. Take a pencil and strike the cups sequentially. The sound generation by each cup will be different. Why is it so?

Apparatus: Two aluminium tins of the same size, two small galsses, water, thermometers, black paint, etc. : Procedure: Paint the outer surface of one tin black paint, and let it dry. Then in both tins, place one glass, each filled with water at the same temperature. cover the tins with lids. Keep them in the sun for two hours. Now measure the temperature of the water in the glasses in the two tins. What is the reason for the difference in the temperature?