Transcript Measuring with Barometers and Manometers

DO NOW:
1. Convert 770 mm Hg  atm
2. Convert 100,900 Pa  atm  mm Hg
Measuring
with Barometers and Manometers
What is atmospheric pressure?
The pressure exerted by the
air in the atmosphere is called
atmospheric pressure. It is
a result of the fact that air has
mass and is attracted by
Earth’s gravity. This attraction
produces a force. The force
exerted on a unit area of the
Earth’s surface is atmospheric
pressure.
We are used to living at 1 Atm of
pressure, so we rarely even take
notice of it. We normally don't feel
the pressure on us because the human
body is primarily made up of liquid,
and liquids are basically noncompressible. At times, however, we
do notice changes of pressure,
primarily in our ears. You may
have noticed your ears "popping“
when flying, driving in the
mountains, or even going up and
down in elevators. This is because
our ears have an air space in them,
and air, like all other gases, is
compressible.
BAROMETERS
You can measure the pressure of the atmosphere with a
barometer.
A mercury barometer is a glass tube that is filled with
mercury, and then inverted into a reservoir of
mercury. The mercury in the tube immediately seeks a
height so that the pressure exerted on the surface of
the mercury in the reservoir is exactly balanced by the
pressure exerted by the mercury column. The height
of the mercury column that will be balanced by a
pressure of exactly 1 atmosphere is 760 millimeters
(mm) at sea level.
Mercury Barometer
MANOMETERS
You can measure the pressure in a closed container.
A simple manometer can be made using a U-shaped
glass tube filled with mercury. One end of the tube
opens into the container in which the gas pressure is to
be measured. The other end of the tube is open to the
surrounding atmosphere. To determine the pressure
in the container, calculate the difference between
atmospheric pressure and the pressure in the
container (the difference between the heights of the
two mercury columns).
U-Tube Manometer
Measuring the Pressure of
Confined Gases
A.
Measuring the Pressure of
Confined Gases
B.
Measuring the Pressure of
Confined Gases
C.
Manometer Practice Problems
A gas container is fitted with
an open-end manometer.
The level of the manometer
is 15mm lower on the open
side. Using a laboratory
barometer, you find that the
atmospheric pressure is
750mmHg. What is the
pressure in atmospheres, of
the gas in the container?
A soccer ball is attached to
an open-end manometer.
The mercury level in the
manometer is 10mm
lower on the side attached
to the ball than on the
side open to the
atmosphere. Atmospheric
pressure has already been
determined to 770 mmHg.
What is the gas pressure
in the ball in mmHg?
Suppose you are measuring
the pressure inside a sealed
cabinet using an openended manometer. The
atmospheric pressure is
662.4 mmHg. If the mercury
level on the side open to the
atmosphere is 3.6mm higher
than the side attached to
the cabinet, what is the
pressure inside the cabinet
in units of kPa?
An open manometer is
filled with mercury. The
mercury level is 12 mm
higher on the side open to
the atmosphere. What is
the total pressure of the
gas, in kPa, if the
atmospheric pressure is
752.4 mm Hg?
An open manometer is
filled with mercury and
connected to a container
of hydrogen gas. The
mercury level is 57 mm
higher in the arm of the
tube connected to the
hydrogen. If the
atmospheric pressure is
748.6 mm Hg, what is the
pressure of the hydrogen
gas, in atmospheres?
An open manometer
connected to a tank of
argon has a mercury level
83 mm higher in the
atmospheric arm. If the
atmospheric pressure is
576.8 mm Hg, what is the
pressure of the argon in
kPa?