Page 103 - Physics - XI

So, P (pressure of enclosed air) = H ± h (where, H is atmospheric pressure)
H
A C 100
Y 90
h 80
X Hg 70 Set-
Hg square
60
B D Metre scale 50
40 Hg
30
20
10

Fig. 3.2: Pressure of air in tube Fig. 3.3: Measuring the level of mercury
by using set-square

3. When the closed tube is not graduated, the volume can be found as follows:
Volume of air in tube = Volume of air in Length PR – Volume of air in curved portion PQ

4. The radius (r) of the tube can be found with the help of a Vernier Calliper.
Volume of curved portion = Volume of hemisphere of radius r

1 4 2 r P
= r 3 r 3 l Q
2 3 3 Air
Volume of PQ = πr × r = πr 3 R
2
Hg
Error in volume = Volume of PQ – Volume of curved portion
A
2
1
= r r r 3
3
3
3 3
Fig. 3.4: Volume of trapped
1
1
Correction in length = r PQ air in tube CD
3 3
This should be subtracted from the measured length l.
5. Note the room temperature by using a thermometer.
6. Note the atmospheric pressure by using Fortin's barometer.

7. Set up the plank of Boyle's law apparatus vertically by adjusting levelling screws and spirit level.
8. Adjust the height of tube CD so that mercury level in both the tubes become same.

9. After that, note down the volume of air in tube AB.
10. Raise the tube CD by about 2 cm.
11. Note down the higher level of mercury in tube AB.

12. Note down the reduced volume of air in AB.
13. Note down the mercury level in CD.

14. Further raise the tube CD by about 2 cm and repeat the above steps.
15. Repeat the previous steps a few more times.

16. Now, lower the tube CD by about 2 cm.

101