JAMB - Physics (1979 - No. 41)
An air column 10cm in length is trapped into the sea end of a capillary tube by a 15cm column of mercury with the tube held vertically as shown above. On inverting the tube the air column becomes 15cm long. The atmospheric pressure during the experiment is
90cm
76cm
75cm
60cm
50cm
Explanation
Let X represent the atmospheric pressure
with tube upright,P1 = ( x + 15)cm, L1 = 10cm
with tube inverted P2 = ( x - 15)cm, L2 = 15cm
using Boyle's law i.e P1V1 = P2V2
(x + 15)10 = (x - 15)15 = 10x + 150 = 15x - 225
15x - 10x = 150 + 225
5x = 375
x = \(\frac{375}{5}\)
= 75cm
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