Question

How will you show that there is vacuum above the surface of mercury in a barometer? What name is given to this vacuum?

Answer 1

The space above mercury is a vacuum. This empty space is called 'Torricellian vacuum'.

 This can be shown by tilting the tube till the mercury fills the tube completely. Again when the mercury column becomes stationary, the empty space is created above the mercury column. If somehow air enters into the empty space or a drop of water gets into the tube, it will immediately vaporize and the air will exert pressure on mercury column due to which the barometric height will decrease.