Use a magnifier to look closely at the thermometer from the front and from the side. Look at the bulb and the thin tube which contain the red liquid. Place the thermometer in hot water and watch the red liquid. Keep it in the hot water until the liquid stops moving. Now put the thermometer in cold water. Keep it in the cold water until the liquid stops moving.
The red liquid goes up in hot water and down in cold water. Students will have an opportunity to relate these observations to an explanation on the molecular level, of why the liquid moves the way it does. If you have time, you can have students pick a temperature somewhere between the temperature of cold water and hot water and then attempt to combine an amount of hot and cold water to achieve that temperature in one try. They can see how close they can get. Give students time after the activity to record their observations by answering the following questions on their activity sheet.
Once they have answered the questions, discuss their observations as a whole group. When heated, the molecules of the red liquid inside the thermometer move faster. This movement competes with the attractions the molecules have for each other and causes the molecules to spread a little further apart.
They have nowhere to go other than up the tube. When the thermometer is placed in cold water, the molecules slow down and their attractions bring them a little closer together bringing them down the tube.
The red liquid is contained in a very thin tube so that a small difference in the volume of the liquid will be noticeable. The large outer tube has two purposes—to protect the fragile inner tube and act as a magnifier to help you better see the red liquid. Note: Alcohol molecules are composed of different atoms, but in the model shown in the animation the molecules are represented as simple red spheres.
Show the molecular model animation Heating and Cooling a Thermometer. Point out that when the thermometer is heated, the molecules move faster, get slightly further apart, and move up the tube. When the thermometer is cooled, the molecules move more slowly, get closer together, and move down the tube. Help students realize that the attractions the molecules in the thermometer have for each other remain the same whether the thermometer is heated or cooled.
The difference is that when heated, the molecules are moving so fast that the movement competes with the attractions, causing the molecules to move further apart and up the tube. When cooled, the movement of the molecules is slower and does not compete as much with the attractions the molecules have for one another. This is why the molecules in the thermometer move closer together and down the tube.
Project the image Molecules in A Thermometer. In the drawing, lines have been added to indicate the level of the liquid in each tube. In reality, there is no line. The red liquid inside of a thermometer is alcohol. Red dye is used to color the clear alcohol so that someone is able to easily read the thermometer.
An alcohol thermometer is used to measure the temperature of extreme cold places. Alcohol thermometer can measure the temperature of — Celsius to It is transparent; therefore, it has to be coloured before it is used. It has low specific heat capacity. When heated, the molecules of the liquid in the thermometer move faster, causing them to get a little further apart. When cooled, the molecules of the liquid in the thermometer move slower, causing them to get a little closer together.
This results in movement down the thermometer. The mercury pools in the bulb, but when it heats up, it expands. A well made, trusted thermometer is based on the fact that most substances expand when heated and contract when cooled.
It has a reservoir of a certain liquid, known to swell and shrink precisely with exact degrees. Changing temperature causes the liquid in the reservoir to rise and fall inside a bored hole in the glass tube. The record is read on a scale of rising degrees marked on or beside the tube. The modern age needed to measure objects hotter and colder than fevers and normal weather temperatures. But the reliable old thread of mercury refused these extra duties, especially the cold ones.
At minus 30 degrees Fahrenheit, liquid mercury freezes solid. When wintry weather dips to this point the silvery thermometer thread cannot budge up or down. But a half mixture of alcohol and water stays liquid down to 58 below zero, This mixture works well in thermometers used in extra cold climates.
Extra gadgets were added to make the reliable old mercury thermometer more useful. Electric wires were sealed into the glass bulb or tube and connected to switches for turning the current on and off.
A talented thermometer of this sort can be geared to turn on i3arms, start or stop machines or act as a thermostat. But science and industry need to measure much wider temperature ranges. Some super thermometers use gases under high pressure; others use electric current. Astronomers take the temperatures of the distant heavenly bodies with an electrical gadget of complicated wire loops. Why does thermometer mercury sometimes look red?
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