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Measuring Temperature in the Lab: Instruments & Process

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  • 0:05 What Temperature Measures
  • 3:11 Measuring Temperature in a Lab
  • 5:51 Lesson Summary
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Lesson Transcript
Instructor: Elizabeth (Nikki) Wyman

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

In this lesson, discover what temperature is a measurement of while learning how to properly measure temperature in a lab. Learn about the important instruments needed for this essential lab skill.

What Temperature Measures

It's early in the morning. The alarm goes off and it's time to get up, but you feel horrible! Your cheeks and forehead are burning and your body aches. Seems like you might have a fever.

Fevers happen when the body elevates its own temperature above 98.6 degrees Fahrenheit to try to cook out any germs that are making it sick. So the best way to determine if you have a fever is to take your temperature!

If you've ever had your temperature taken, you've likely had to put a thermometer under your tongue and wait for at least a minute before you can get an accurate reading. Why do you think you have to wait?

Before I answer that question, let's make sure we have a good understanding of what temperature is actually a measurement of.

Everything is made of teeny tiny particles. These particles are energetic and move around. The more these particles move, the more energy they have. The less these particles move, the less energy they have. This energy in motion is called kinetic energy. Temperature is the measurement of the average kinetic energy of the particles in a substance, or scientifically speaking, a system.

A thermometer is a clever device for measuring the average kinetic energy of a system. Glass thermometers contain a liquid that expands when it is warmed and contracts when it is cooled. Digital thermometers contain a device called a thermoresistor. A thermoresistor is a little electronic piece that conducts electricity when heated. The more electricity conducted, the higher the temperature reading.

Two more facts and we'll move on. First of all, there is no such thing as a cold particle -- being cold only means that there is an absence of kinetic energy. Second, kinetic energy always moves from a warmer object to a cooler one. So if you go outside in a t-shirt and shorts in freezing weather, you get cold because your body's kinetic energy gets transferred to the cool air, leaving you with an absence of kinetic energy! If you rush back inside and sit by the fire, the kinetic energy from the fire will transfer back to you, the relatively cool object in the room. The transfer of energy continues until an equilibrium is reached and both objects have the same average kinetic energy.

The same thing happens when we use a thermometer. When not in use, the thermometer is taking the reading of its ambient environment. When you place it under your tongue to see if you have a fever, energy from your body is transferred to the thermometer. If you are using a glass thermometer, the liquid inside is expanding as it gets energized. If you are using a digital thermometer, the thermoresistor is conducting electricity. Once equilibrium is reached, a final temperature reading can be taken.

Returning to our initial question, you have to wait to see your temperature because you have to keep that thermometer under your tongue until equilibrium is reached and you get an accurate reading. 103 degrees Fahrenheit?! You should go back to bed.

Measuring Temperature in Lab

Now that your fever is gone and you're healthy again, you can return to science lab. Today's assignment: measuring temperature.

In the physical sciences we usually measure temperature in terms of degrees Celsius (C) or degrees Kelvin (K). So in science class it is typical to measure things in terms of Celsius or Kelvin.

The size of one Kelvin is the same as one degree Celsius; however, the scales start in different places. Zero degrees Celsius equals the freezing point of water. The freezing point of water in Kelvin, however, is 273.15. If you need to convert between Kelvin and Celsius remember this simple formula: temperature in Kelvin equals degrees Celsius plus 273.15.

K = °C + 273.15

Fahrenheit (F) is a temperature measurement used in the engineering sciences. In the United States, we use Fahrenheit every day to talk about the weather or baking temperatures or to measure our body temperature.

The formula that converts between Fahrenheit and Celsius is quite complicated: F = C(9/5) + 32

In lab, you usually have the option to measure temperature in K, C or F. It's best to measure in Celsius or Kelvin because many calculations and equations require that temperatures be in terms of C or K. If you stay consistent, you don't have to go through this pesky conversion.

When you are taking the temperature of a substance, make the following precautions:

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