Evangelista Torricelli is credited with several inventions, the most notable of

Question

Evangelista Torricelli is credited with several inventions, the most notable of which is the mercury barometer. A diagram of the device is shown below. Torricelli took a glass tube and filled it to the brim (with no air inside) with mercury. He then flipped it upside down after placing it in a pool of mercury. Upon doing so, some small amount of mercury drains out of the tube and into the pool, leaving behind a small volume at the closed end of the tube with no air resident in that volume (aka it’s a vacuum). Note: The density of mercury is 13.6 times as dense as water.

A.) What is the pressure at the surface of the mercury near the top of the tube at point A?

B.) What is the pressure at point B at the bottom of the tube’s column?

C.) What is the pressure at the surface of the mercury pool? (assume standard elevation)

D.) To what height does the mercury column within the tube stand above the pool’s surface?

E.) If the device were adjusted to accommodate the use of water instead of mercury, how tall would Torricelli’s barometer need to be to adequately measure atmospheric pressure?

Explanation / Answer

A) normal air pressure

1atm

B) p' = p'+hpg ( P water*13.6 = P macury)

P' = 1*10 5 - h *1000* 13.6 * 9.8 N/m2

C) normal air pressure

1atm

D) h = 100000/1000* 13.6 *9.8

=0.75m

E) h(water) = 100000/1000*9.8

=10.2m

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