ICSE Class 9 Answered
(a) Barometer
(b) Take a glass tube 1m long, closed at one end. Fill it completely with mercury. By placing thumb on the open end of the tube, invert the tube into a bowl of mercury and then remove the thumb. It is seen fairly large length of mercury is supported in the tube. On measuring, length of mercury from its level in tube to the level of mercury in the bowl, it is found to be 76cm at sea level. This length is equivalent to atmospheric pressure.
(c) Precautions:
1. The barometer tube should be perfectly clean and dry.
2. The mercury should be pure and dry.
3. No air bubble should be left inside the tube filled with mercury.
4. Record the vertical height of the mercury column in the tube, by holding the tube in an upright position.