What is a thermometer?

Hint: The word ‘thermo’ is derived in relation to heat or thermal energy. The physical quantities such as temperature can be measured using instruments which employ some other physical properties that can be standardized for a true measure.

Complete step-by-step solution
We have to understand the physical conditions around us for a comfortable living. The knowledge of the temperature changes in seasons let us prepare to live a better life in those harsh climatic conditions of the year. A thermometer is such an instrument that we use in our daily life to measure the degree of hotness or coldness. There are different types of thermometers depending on their use. Some of them are:
1). Clinical thermometers: These are small mercury thermometers, which are used to measure the human body’s temperature. It has a very short range of temperatures and usually comes in Fahrenheit.
2). Laboratory thermometers: These are thermometers used in laboratories to measure the temperature of samples which are spread over a wide range. They usually come to the Celsius scale.
There are also digital thermometers available today, which use special heat sensors for temperature detection. Even smartphones are available with these sensors making their lives better and easier.
So thermometers are instruments, which aid in temperature reading.
The mercury thermometers are the oldest and still widely used thermometers.

Note: The mercury thermometers work on the special property of mercury. The element mercury is a liquid at room temperature. Also, it has a high coefficient of thermal expansion. The metal can expand very fast with slight changes in temperature. These expansions are calibrated and used as scales in thermometers.