Comprehension STOP Use your dictionary to find out the meaning of the bold words below. How Does a Thermometer Work?
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A thermometer is a device used to measure temperature. How does it work?
The bulb thermometer is the most widely known type of thermometer. It is made with a narrow glass tube that has a small bulb at its base containing fluid. The thermometers used in laboratories usually contain a silvery liquid called mercury. Mercury is the only metallic element that is liquid in its standard state.
Bulb Temperature markings
The volume of a liquid changes depending on its temperature. Cold temperatures cause it to take up less space and warm temperatures mean it takes up more space. All liquids share this property. Mercury is used in thermometers because it has a higher boiling point and a lower freezing point than most other liquids. This means that it needs to be very hot before it will boil and very cold before it will freeze. However, mercury is toxic when it comes into contact with the skin. As a result, alcohol or galinstan (another liquid element) have become more widely used in bulb thermometers. Both also have a high boiling point and a low freezing point.
As the thermometer’s bulb is small, the liquid inside it quickly reaches the temperature of the substance being measured. The liquid then expands or contracts depending on how hot or cold the substance is. We can then look at the markings on the side of the thermometer to gain an accurate reading of the temperature.
Most people now use digital thermometers, which are are safer and easier to read, and work faster.
How do we measure temperature?
There are two different units of measurement for temperature: Fahrenheit and Celsius. In Ireland, we use the Celsius scale (°C). Celsius measures the freezing point of water as 0°C and the boiling point of water as 100°C. We define room temperature as the temperature at which a room feels neither warm nor cold when wearing typical indoor clothing. This scale ranges from 15°C to 25°C. Normal body temperature is defined as 36.5°C to 37.5°C.
What are thermometers used for?
Thermometers have many uses. They are used to determine road temperatures in order to predict freezing, to measure optimum temperatures for cooking, to record body temperatures in medicine and to forecast the weather.
Thermometers have many different uses in our everyday lives. They are important in cooking, in health and in scientific experiments. Reading a bulb thermometer is an important skill. However, this is becoming less popular due to safety concerns.
68 Mercury Glass tube
Unit 12 | Explanatory Text 1
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