How would changing the diameter of a barometer not change the pressure reading?

Question

How would changing the diameter of a barometer not change the pressure reading?

Answer 1

what kind of barometer?

Well, regardless, pressure is force per unit area. If you increase the area affected by the pressure, you also increase the force. By increasing the diameter of the barometer, you get more force for the increased amount of stuff in the barometer that's displaced and measured.

Vice versa for decreasing the diameter.

^^ It really depends on the type of barometer and the way it's built, and which diameters are changed in some types. For your situation to be true, the change in area exposed to pressure must be proportional to the change in pressure measuring media (eg. mercury in mercury barometers).

Answer 2

If you could place a dish of mercury and an inverted 30-inch glass tube dipped in the mercury within a bell jar maintained at a perfect vacuum, drawing a vacuum in the inverted tube (using a vacuum pump?) would not draw mercury up into the tube.  The entire weight of a column of atmospheric air (up to the edge of space) exerts a pressure of 14.7 psig on every square inch of surface which has enough force to drive a column of mercury about 30 inches up into a vacuum filled tube (as in a barometer).  If the barometer tube has a cross-sectional area of one square inch there will be a driving force of 14.7 pounds and if the area is two square inches there will be a driving force of 2 x 14.7 pounds = 29.4 pounds.

Answer 3

The atmospheric pressure(P) at any place is given by P=Hdg

where 'H' is the height of the mercury column,'d' is the density of the liquid used(mercury) and g is the gravity.

Here you can note that the area of the tube(or diameter) do not find a place and hence the pressure is independent of area(or diameter)

Answer 4

They are calibrated to measure ambient pressure.  Ambient pressure is the same no matter how large the sample measured. The same with a thermometer or a hydrometer.  Ambient temperature and ambient humidity do not change with the size of the instrument.

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Answer 5

Changing the diameter changes the surface area.

Air pressure acts upon the whole exposed surface.

So increased area, more pressure, supports more mercury.