70 JUNIOR GRADE SCIENCE 



55. Describe a simple barometer. Why is mercury used ? Would any 

 other liquid serve ? How may a barometer be used for measuring heights 

 of mountains ? 



56. Explain as clearly as you can why the height of the barometer gives 

 a measure of the pressure of the atmosphere. 



57. How would the position of the mercury in a simple barometer be 

 affected (1) if the tube were sloped ? (2) if the tube had a very irregular 

 section, wide in some places and narrow in others ? Give full reasons for 

 your answers. 



58. A faulty barometer contains some air above the mercury. Will 

 the extent of its rise and fall be greater or less than the corresponding 

 movements of a correct barometer ? Give the reason for your answer. 



59. A barometer tube stands vertically with its open end below the surface 

 of mercury. The mercury stands at the same level inside and outside 

 the tube, and the closed end of the tube is 20 inches above this level. If 

 the tube is now raised until the mercury stands 4 inches higher inside than 

 outside, find the height of the closed end above the outside level, the height 

 of the barometer being 29 inches. 



60. State the law which governs the change of volume of a given mass 

 of gas under varying pressure, at constant temperature. Who discovered 

 this law ? 



61. State Boyle's Law. 



A U-tube of uniform bore has one end closed and the other open. Mercury 

 is poured in, and when it stands at the same level on the two sides the length 

 occupied by air on the closed side is 12 inches. More mercury is then poured 

 in till the level on the closed side rises by 1 inch. What is now the difference 

 of level on the two sides and how much mercury was poured in between 

 the two observations ? The height of the barometer is 30 inches. 



62. Describe a way of finding out how the pressure of a quantity of 

 air changes when the air is compressed into smaller volume. Draw a sketch 

 of the apparatus used, and state the result which is arrived at. 



63. If you were supplied with a barometer tube, a deep reservoir full 

 of mercury and a measuring scale, how would you study the relation between 

 the pressure and volume of a quantity of air at constant temperature ? 



64. Being provided with a U-tube of uniform bore with one end closed, 

 a measuring scale, and some mercury, how could you determine the atmo- 

 spheric pressure ? 



65. How would you examine the relation between the volume and 

 pressure of a gas, the temperature being constant ? Give a sketch of the 

 apparatus used. 



