A body cools from 80 ° C to 70 ° C in 5 minutes and to 62 ° C in the next 5 minutes. Calculate the temperature of the surroundings.

By using Newton's law of cooling, - T f - T i t = K • T f + T i 2 - T ° here T ° is tempreature of surrounding - ( 70 - 80 ) 5 = K 70 + 80 2 - T ° ............(1) - ( 62 - 70 ) 5 = K 70 + 62 2 - T ° .............(2) Divide Eq.(1) by Eq. (2), we get 2 8 5 = K ( 75 - T ° ) K ( 66 - T ° ) T ° = 30 ° C

State any ‘four’ assumptions of the kinetic theory of gases.

1. A gas consists of very large number of extremely small particles known as molecules. 2. The intermolecular force of attraction between gas molecules are negligible. 3. Molecules are always in the state of random motion, i.e., they are moving in all possible directions with all possible velocities. This state is called molecular chaos. 4. Between any two successive collision, a molecule travels in a straight line with constant velocity. It is called free path.