How Does a Thermometer Work?
An application of simple physics
Nowadays, you often see thermometers. “ Thermometer” — as the name suggests — is used to measure the temperature of the environment / object. There are various types of thermometers, such as laboratory/medical thermometers, digital thermometers, and so on. For this time, I will focus the discussion on laboratory/medical thermometers.
Physics approach
As you learned in school, objects around you can expand when exposed to heat. These objects expand at different rates. Some objects expand very easily, while others are very difficult to expand. One substance that expands easily is alcohol. Just by applying a little heat, the volume of alcohol can increase significantly due to the expansion process. The volatile nature of alcohol is what scientists use to make thermometers. How do they work?
For your information, the increase in the temperature of alcohol is directly proportional to the increase in its volume due to expansion. Suppose in an experiment you observe that if the temperature of alcohol increases by 20°C, its volume increases by 10 cm³. The question is, if the volume of alcohol is increased by 20 cm³, what is the increase in volume? It’s easy. because the volume is doubled, the temperature is also doubled. So, if the volume increases by 20 cm³, then the temperature increases by 2×20°C=40°C.
Now, in the same way, we can label "temperature" for every 1 cm³ increase in volume of alcohol.
In order for the changes that occur in the alcohol to be more easily observed, the alcohol is placed in a capillary pipe. A capillary pipe is a type of pipe with a very small diameter (approximately the diameter of a needle). That way, the change in alcohol temperature can be said to be directly proportional to the change in the height of the alcohol in the capillary pipe.
Alcohol itself can expand to a maximum temperature of 78°C. If the temperature reaches 78°C and the change in height of alcohol in the capillary pipe reaches x cm, then we can label 1°C at a height of x/78 cm on the capillary pipe, label 2°C at a height of 2x/78 cm on the capillary pipe, label 3°C at a height of 3x/78 cm on a capillary pipe, and so on. In other words, if the height of the alcohol increases by nx/78 cm, we can conclude that the temperature of the alcohol increases by n°C. This problem is the same as "If 10 bags contain 20 apples, how many apples are in 1 bag?". Not too difficult right?
It may sound a bit complicated, but the principle is simple. The thermometer can measure temperature by observing the increase in the height of the alcohol in the capillary pipe.
The components of thermometer
In general, a thermometer consists of 3 main components, namely the tip, capillary pipe, and filling liquid.
Mechanism
Let’s say you want to measure your body temperature with a thermometer. The tip of the thermometer (bulb) is made of a material that is very easy to transfer heat. When the bulb touches your body, heat from your body will flow through the bulb to the alcohol in the capillary pipe. This causes the alcohol to expand and increase the alcohol level in the capillary pipe. Based on the increase in the level of alcohol in the capillary pipe, our body temperature can be determined.
So, that’s how thermometers work. If there are some parts that you don’t understand, don’t hesitate to ask in the response column. In addition, you can also ask questions to me for the next article. Goodbye!
