PHYSICS [2 Mark Question Answer]

In a water pump, on pulling the piston up, the pressure of air inside the siphon decreases and the atmospheric pressure on the water outside increases. As a result, the atmospheric pressure pushes the water up in pump.

When syringe is kept with its opening just inside a liquid and its plunger is pulled up in the barrel, the pressure of air inside the barrel below the plunger becomes much less than the atmospheric pressure acting on the liquid. As a result, the atmospheric pressure forces the liquid to rise up in the syringe.

Water is held inside the dropper against the atmospheric pressure because the pressure due to height column of liquid inside the dropper is less than the atmospheric pressure. By pressing the dropper we increase the pressure inside the dropper and when it becomes greater than the atmospheric pressure the liquid comes out of the dropper.

When air is removed from the balloon, the pressure inside the balloon (which was due to air in it) is much less than the atmospheric pressure outside and hence the balloon collapses.

We do not feel uneasy under enormous pressure of the atmosphere above as well as around us because of the pressure of our blood, known as blood pressure, is slightly more than the atmospheric pressure. Thus, our blood pressure balances the atmospheric pressure.

On mountains, the atmospheric pressure is quite low. As such, nose bleeding may occur due to excess pressure of blood over the atmospheric pressure.

A fountain pen filled with ink contains some air at a pressure equal to atmospheric pressure on earth's surface. When pen is taken to an altitude, atmospheric pressure is low so the excess pressure inside the rubber tube forces the ink to leak out.

Factors that affect the atmospheric pressure are: (i) Height of air column (ii) Density of air

(i) In a mine, reading of a barometer increases. (ii) On hills, reading of barometer decreases.

Aneroid barometer has no liquid and it is portable. It is calibrated to read directly the atmospheric pressure.

Water is not a suitable barometric liquid because: (i) The vapour pressure of water is high, so its vapours in the vacuum space will make the reading inaccurate. (ii) Water sticks with the glass tube and wets it, so the reading becomes inaccurate.

Two advantages of using mercury as barometric liquid: (i) The density of mercury is greater than that of all the liquids, so only 0.76m height of mercury column is needed to balance the normal atmospheric pressure. (ii) The mercury neither wets nor sticks to the glass tube therefore it gives the correct reading.

The thrust exerted per unit area of the earth surface due to column of air, is called the atmospheric pressure on the earth surface.

Two uses of barometer: (a) To measure the atmospheric pressure. (b) For weather forecasting

It is the atmospheric pressure acting on the surface of the mercury in the trough that supports the vertical mercury column. Hence, barometric height is used as unit to express the atmospheric pressure.

As the pressure inside the bell jar has decreased, the air pressure around it is more. So, in order to balance the pressure differences in its surroundings, The balloon inflates which means pressure inside it increases. Therefore, the pressure inside the balloon increases and inside the bell jar decreases.

The tip of an allpin is made sharp so that large pressure is exerted at the sharp end and it can be driven into with less effort.

Thrust is the force applied on a surface in a perpendicular direction and it is a vector quantity. The effect of thrust per unit area is pressure, and it is a scalar quantity.

Hydraulic press works on principle of hydraulic machine. It states that a small force applied on a smaller piston is transmitted to produce a large force on the bigger piston. Use: It is used for squeezing oil out of linseed and cotton seeds.

The principle of a hydraulic machine is that a small force applied on a smaller piston is transmitted to produce a large force on the bigger piston. Hydraulic press and hydraulic brakes work on this principle.

Two applications of Pascal's law: (i) Hydraulic press (ii) Hydraulic jack

The water jet through A will have a larger horizontal range because the water pressure is more at that point. While B is just below the surface so water will come out of it without any significant pressure.

The sea divers need special protective suit to wear because in deep sea, the total pressure exerted on the diver's body is much more than his blood pressure. To withstand it, he needs to wear a special protective suit.

The pressure exerted by a liquid increases with its depth. Thus as depth increases, more and more pressure is exerted by water on wall of the dam. A thicker wall is required to withstand greater pressure, therefore, the thickness of the wall of dam increases towards the bottom.

Due to dissolved salts, density of sea water is more than the density of river water, so pressure at a certain depth in sea water is more than that at the same depth in river water.

Pressure at a point in a liquid depends upon the following three factors: (i) Depth of the point below the free surface. (ii) Density of liquid. (iii) Acceleration due to gravity.

A solid exerts pressure only on the surface on which it is placed, i.e. at its bottom, but a fluid exerts pressure at all points in all directions.

Due to its weight, a fluid exerts pressure in all directions; the pressure exerted by the fluid is called fluid pressure.

Wide wooden sleepers are placed below the railway tracks so that the pressure exerted by the rails on the ground becomes less.

It is easier to cut with a sharp knife because even a small thrust causes great pressure at the edges and cutting can be done with less effort.