Question

why does the ink from the fountain pen leak at higher altitude

Answer 1

The pressure at higher altitudes iscomparatively less, so to equalize the pressure difference ink starts moving out from the pen which has a relatively highpressure. Same applies to tooth paste as well as bleeding from nose at suchaltitudes.
The atmospheric pressure decreases with altitudebecause gas molecules which make up the air concentrate near lower altitude in response to Earth’s gravity. Hence, air pressure is low at higher altitudes. Fountain pen brought to higher altitudes from lower altitude regions contain air at high pressure (equal to that of the low altitude region it is brought from). Due to this difference in air pressure, the air inside the pen forces the ink to come out. This equalizes the air pressure inside and outside the pen (Boyle’s Law: PV=constant). Hence the pen leaks. a fountain pen have rubbery tube at it,s end in which the ink is stored , the tension in this tube pushes the ink out of the tip and the atmospheric pressure resists the outflow of the ink . The relative magnitude of these forces ensures that right amount of ink is flowing on the ground level but as we go on mountains the atmospheric pressure decreases but the tension in the tube remains the same and because of which the fountain pen leaks.

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