Question

If a student places barometer in a lift falling under gravity how the barometer reading will change

Answer 1

Under normal conditions when the elevator is accelerating upwards the reading in the barometer will be less than 76cm (air pressure is same as external) but as acc. to question the pressure is 76 cm means that the air is applying more pressure to lift the liquid to a height of 76cm.so the air pressure in the lift is higher than the normal(76 cm).

the liqiud becomes heavier m*(g+a) when the lift accelerating upwards. so it requires more more pressure from the air onto the liquid to rise at the height of 76 cm.

Answer 2

If a student places a barometer in a lift falling under gravity, the liquid column inside the barometer will shoot up at its maximum level.

1) A baromoter contains a liquid which has its own weight.

2) when a lift is moving down the weight of fluid acting on the barometer is equal to m*(g-a) , where a is the acceleration during descent.

3) But when the lift is falling under gravity, it is a condition of free fall.

4) So, the liquid column does not possess any weight of its own.

5) Therefore, the atmospheric pressure pushes the column up into the barometer as there is some pressure in the container.