Question

How does a barometer work? Is the column of mercury in a barometer shorter when it is on a mountaintop or at sea level? Explain.

Short answer

The mercury column is shorter on a mountaintop due to lower atmospheric pressure.

Step-by-step solution

Understanding Atmospheric Pressure

A barometer measures atmospheric pressure, which is the force exerted by air molecules on a surface. Atmospheric pressure decreases with increasing altitude because there is less air above the surface at higher altitudes.

Function of a Mercury Barometer

In a mercury barometer, atmospheric pressure pushes down on a reservoir of mercury, causing the mercury to rise in a tube. The height of the mercury column is a measure of atmospheric pressure.

Effect of Altitude on Mercury Column

At higher altitudes (such as on a mountaintop), the atmospheric pressure is lower because there is less air above. Therefore, the mercury column in a barometer will be shorter on a mountaintop compared to at sea level.

Comparison at Different Altitudes

Sea level has higher atmospheric pressure due to the larger volume of air above. Consequently, the mercury column at sea level will be taller compared to the mercury column at higher altitudes like a mountaintop.

Key concepts

atmospheric pressure

Atmospheric pressure is the force per unit area exerted by the weight of the air above a surface. Air molecules are constantly moving and colliding with surfaces, creating this pressure. At sea level, the atmospheric pressure is higher due to the larger number of air molecules above. As altitude increases, there are fewer air molecules above the surface, resulting in lower atmospheric pressure. Understanding this concept is crucial for grasping how barometers measure pressure and how altitude affects these measurements.

• Air pressure decreases with height.
• More air above means higher pressure.
• Less air above means lower pressure.

mercury barometer

A mercury barometer is a tool used to measure atmospheric pressure. It consists of a glass tube closed at one end, and open at the other, which is submerged in a reservoir of mercury. Atmospheric pressure acts on the surface of the mercury in the reservoir, causing it to rise or fall inside the glass tube. The height of the mercury column within the tube indicates the atmospheric pressure. Mercury is used because it has a high density, allowing for a smaller and more manageable barometer size compared to other liquids.

• Mercury barometer measures pressure by mercury level.
• Atmospheric pressure causes mercury to rise/fall.
• Mercury's high density makes it ideal for barometers.

effect of altitude on pressure

Altitude significantly affects atmospheric pressure. As you ascend to higher altitudes, the number of air molecules decreases, reducing the atmospheric pressure. This decrease in pressure also affects the height of the mercury column in a barometer. For example, at higher altitudes, there is less atmospheric pressure to push down on the mercury reservoir, resulting in a shorter mercury column. This change occurs because the atmospheric pressure at higher altitudes is lower due to the reduced amount of air above.

• Higher altitude means lower pressure.
• Mercury column shortens as altitude increases.
• Less air above causes lower pressure.

altitude comparison

Comparing the mercury barometer readings at different altitudes helps illustrate the effect of altitude on atmospheric pressure. At sea level, the air pressure is higher because of the larger column of air exerting force on the mercury. This results in a taller mercury column. On a mountaintop, however, the atmospheric pressure is lower because there is a smaller column of air above. Consequently, the mercury column is shorter. This principle is crucial for understanding how weather and altitude can affect atmospheric pressure readings.

• Sea level: higher pressure, taller mercury column.
• Mountaintop: lower pressure, shorter mercury column.
• Mercury barometer readings vary with altitude.