Galileo Thermometer

Classical Mechanics Level 1

A Galileo thermometer uses fluid density to display the temperature. The small bulbs are typically filled with water, food coloring, and sometimes alcohol to a specific density. The bottommost floating bulb displays the approximate temperature. (The blue bulb in the picture shows the approximate temperature of 24 degrees Celsius.)

Which answer choice has the biggest effect on the bulbs' movement?

Changes in the amount of light cause changes in the surrounding fluid's volume Changes in air temperature cause changes in the surrounding fluid's mass Changes in air temperature cause changes in the surrounding fluid's volume Changes in desk temperature cause changes in the surrounding fluid's volume

Brack Harmon by Brack harmon , 18, USA

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1 solution

Brack Harmon
May 23, 2018

For example, If the temperature of the air increases, then the fluid temperature increases causing the fluid & the glass to expand. With this expansion the volume of the fluid will increase causing it's density to decrease. Bulbs with a heavier density than the surrounding fluid will sink to the bottom.

3 Helpful 0 Interesting 0 Brilliant 0 Confused

Hello I'm new and honestly not very good yet at this stuff, but can you explain why change in the desks temp wouldn't change its volume.

Jacob Strohmeyer - 3 years ago

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Because Glass is insulator

Aryan Sanghi - 3 years ago

The problem asks for what has the biggest effect on the bulbs’ movement. For example if the air temperature increases 2 degree Celsius (now 26 degrees), The blue bulb would sink. This wouldn't happen if the desk was heated 2 degrees Celsius because only the thermometer's base touches the desk. Also, we were all beginners to start out. With practice comes learning.

Brack harmon - 3 years ago

It's normal not to find it clear because there are quite a few factor which influence the answer.

As mentioned glass is an insulator. Furthermore wood is also a poor heat conductor and, "most of the time", the change in air temperature is the main cause for the desk temperature to change. The chances that the floor would be so much cooler as to beat the full length of wood in the desk (somewhere near 1 m) are small. In case you never tried, a house with 1m thick wooden walls is actually pretty well insulated from the outside.

In extreme cases it could happen that the desk has the most influence. For example, if your desk is made of aluminum (or even better silver) and bathing in liquid helium while a sheet of warm air is flowing above, I'm pretty sure the desk would make a big difference. Also, if the window in the room is open so that fresh air permanently flows around the glass and your aluminum/silver desk is being heated to high temperatures, then I would also guess that the desk would have a significant effect in heating up the liquid.

So it's pretty unclear where the limit is, but I believe that for a wooden desk under common circumstances, the desk is not having much of an effect.

Antoine G - 3 years ago

Thanks to all of you for replying and explaining.

Jacob Strohmeyer - 2 years, 12 months ago

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