A thermometer is a device which used to measure temperature. There are many different kinds of thermometers, some more suitable than others to be used in certain situations.
Laboratory Thermometer
- Can contain mercury or alcohol
- The temperature range depends on which liquid is used
- For mercury lab thermometers, the range is $-39\degree C$ to $357\degree C$
- For alcohol lab thermometers, the range is $-115\degree C$ to $78\degree C$
- We thus wouldn’t use an alcohol thermometer to measure the temperature of water which we are taking up to boiling point ($100\degree C$). In colder climates, alcohol thermometers are preferable
- Mercury thermometers are more sensitive to and also respond more quickly to temperature changes when compared to alcohol thermometers
- The glass surrounding the capillary tube is thick and acts as a magnifying glass
Clinical Thermometer
- Smaller than laboratory thermometer
- Has a constriction in the capillary tube
- The constriction serves to prevent the mercury above it from retreating into the reservoir
- This mercury is reunited with the rest in the bulb when the thermometer is shaken
- The range is usually between $35\degree C$ and $42\degree C$
- This short range allows for the thermometer to be more sensitive to changes in temperature (a small difference in temperature produces a large change in mercury length)
- This greater sensitivity is achieved by a narrow bore (think about 1 ml water rising up into a straw as opposed to 1 ml rising up into a large pipe)
Thermocouple
- This consists of two dissimilar metals coming together to form an electrical junction
- When there is a temperature difference, a small voltage is produced
- This voltage is related to the temperature difference and thus can be used to measure the temperature of one object (placed at the hot junction) relative to another (at the cold junction)
- This temperature dependence is called the Seebeck effect
