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DENJIRO: Perhaps you’ve been measuring your temperature more often than you used to because of COVID-19. One common type of thermometer that’s being used these days are infrared thermometers. It’s a contactless thermometer that uses infrared rays. It displays your temperature immediately.
Maybe the thermometer you have at home is an electronic one like this. Let’s look inside it to see how it measures your temperature. Inside the tip that you place under your armpit is a temperature sensor known as a thermistor. Let’s attach the thermistor to a measuring instrument and place it in water. We’ve got a reading. This is the resistance value. Now let’s place the thermistor in hot water.
GIRL: The number went down!
NARRATOR: An electronic thermometer takes the change in resistance value that arises due to the temperature and converts it into body temperature.
DENJIRO: An electronic thermometer starts beeping after a relatively short period and displays your body temperature. This is called a predicted value. Your body temperature is predicted based on how your temperature is rising. If you leave in the thermometer for another ten minutes, it will beep again and display your actual temperature. This is called the actual value.
In the past, people used an analog mercury thermometer. Let’s see how the temperature rises. I’ve put the thermometer in water, and now I’ll add hot water to it. The mercury expands as it gets warm, and that’s why the reading goes up. Now let’s take the thermometer out of the hot water. You can see that the mercury isn’t going down. This is strange, since the temperature should be going down. Let’s zoom in on the part where the tube is narrow. You can see that the mercury is cut off. When the temperature rises, the mercury expands and rises. However, even if the temperature drops, the thermometer displays the maximum temperature since the mercury is cut off. As a result, you’re able to check your temperature for some time after you measure it. Nowadays, thermometers that use liquid metal and not mercury are available.
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