question_answer

  Give reasons (a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called asolid. (d) We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert. Or (a) You want to wear your favorite shirtto a party, but the problem is that it isstill wet after a wash. What steps would you take to dry it faster? (b) It is a hot summer day, Priyanshi and Ali are wearing cotton and nylonclothes respectively. Who do you think would be more comfortable and why?

Answer:

  (a) There is little attraction between particles of gas. Thus, gas particles move freely in all directions. Therefore, gas completely fills the vessel in which it is kept.                                                                                       (1) (b) Particles of gas move randomly in all directions, at high speed. As a result, the particles hit each other and also hit the walls of the container witha force. Therefore, gas exerts pressure on the walls of the container.                     (1) (c) A wooden table has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. Hence, awooden table should be called a solid.                                                               (1) (d) Particles of air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in air, butto do the same through a solid block of wood, we need a karate expert.                                                                                                                               (2) Or (a) We can take (any one or more) the following steps (i) Dry it under the fan. (ii) Use hanger for exposing its larger surface toair. (iii) Dry in sun. (iv) Use iron.                                                                                                                                                                                      (2) (b) Priyanshi would be more comfortable. The reason is that cotton absorbs sweat from the body and provides it a larger surface area for evaporation. Increased evaporation causes more, cooling effect. Nylon does not absorb sweat so the sweat doesnot evaporate and Ali would feel uncomfortable.            (1+2)