Explanation of temperature scales - Succeed in Physical Science. Also refer to Physics, units, multiples, thermometer, Fahrenheit, Celsius, Kelvin, Rankin, freezing, boiling, salt water, metabolism, measurement, Ron Kurtus, School for Champions. Copyright © Restrictions
Temperature Scales
by Ron Kurtus (13 December 2006)
A temperature scale is the determination of a unit of temperature. The scale is established by setting two fixed points as 0 (zero) and 100 and then dividing it into 100 units or degrees. The first major temperature scale was the Fahrenheit scale, which is still used in the United States. Afterwards, the centigrade or Celsius scale was established. Celsius is considered metric and is used throughout most of the world. The Kelvin scale is a variation of the Celsius scale. It starts at absolute zero and is used in scientific measurements and in many heat-related calculations. You can use a formula to convert a temperature in one scale to another.
Questions you may have include:
- How was the Fahrenheit scale determined?
- What are the Celsius and Kelvin scales?
- How do you convert from Fahrenheit to Celsius?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
Useful tools: Metric-English Conversion | Scientific Calculator.
Fahrenheit
Around 1700, a German scientist Gabriel Fahrenheit invented the thermometer by putting water in a thin glass tube. The warmer the temperature, the higher the water went up the tube.
To be able to measure temperature with numbers, Fahrenheit had to determine a unit of measurement. Just as the measurement of weight and length was based on multiples of an arbitrary unit of measurement (the pound, gram, inch, meter), the measurement of temperature is based on an arbitrary unit of measurement—the degree.
Fahrenheit defines units
Fahrenheit used his body temperature as 100° F (100 degrees fahrenheit) and the freezing temperature of saturated salt water as 0° F. He marked those levels on his thermometer and divided the scale into 100 parts for each degree.
Poor choices
The choices of his body temperature for 100° F and the freezing temperature of salt water for 0° F were unfortunate.
Fahrenheit's metabolism was higher than most people, so 100° F for him resulted in 98.6° F as the body temperature for the average person.
Fahrenheit designated the freezing temperature of water saturated with salt as 0° F. But that certainly is not the coldest temperature you can experience in winter weather. It also makes the freezing point of water an awkward 32° F. Since ocean water is not saturated with salt, it freezes at 28° F.
What is more amazing than this poor selection of temperature units is the fact that countries such as Great Britain and the United States embraced that system of measurement. England has since gone to the the Celsius scale, while the U.S. still stays with the Fahrenheit scale.
Metric temperature units
The metric or SI (System International) units of temperature are Celsius and Kelvin.
Celsius
About 20 years after Fahrenheit invented the thermometer, Swedish professor Anders Celsius defined a better scale for measuring temperature. He proposed using the boiling point of water as 100° C and the freezing point of water as 0° C. This made a lot more sense, and it was called the centigrade system. (Centi- means hundred and centigrade means divided into 100 units.)
The centigrade scale was used until the 1960s, when the scientific community renamed it the Celsius system in honor of the inventor. Some people still call it the centigrade scale.
Europe and most of the world measures temperature in Celsius units.
Kelvin
For scientific work with the energy of molecules, it is good to have a starting point where the energy level is at a lowest possible state. This point is called absolute zero.
The Kelvin scale was determined based on the Celsius scale, but with a starting point at absolute zero. Temperatures in the Kelvin scale are 273 degrees less than in the Celsius scale. Thus absolute zero is -273° C and the boiling point of water 100° C is 373 K or 373 kelvins.
Note: There is no degree sign when using the Kelvin scale. Don't ask me why. That is just the way they wanted to do it.
There is also the Rankine scale, which also starts at absolute zero but is based on the Fahrenheit scale. Since most scientific work is done based on the Kelvin scale, the Rankine scale for absolute temperatures is seldom used.
Converting between systems
Because Fahrenheit is used in the United States and Celsius is used almost everywhere else, you may have to convert degrees from one system to another. A simple way of doing that is by using the following conversion application:
Temperature Converter
Enter a number in one box and then Click Here.
Use the reset button to clear the numbers.
If you have to learn to make the calculation by hand, the following equations are used:
Celsius to Fahrenheit
The formula to convert Celsius to Fahrenheit is:
F = 9C/5 + 32
In other words, if C = 100° C (boiling point of water), then
F = (9 x 100)/5 + 32 = 212° F
Fahrenheit to Celsius
The formula to convert Fahrenheit to Celsius is:
C = 5(F - 32)/9
In other words, if F = 50° F , then
C = 5*(50 - 32)/9 = 5*(18)/9 = 10° C
Celsius to Kelvin
Converting from degrees Celsius to Kelvin is simple.
K = C + 273
Thus, if C = 10° C, the Kelvin temperature would be 283 K.
Summary
Temperature is designated as a multiple of a unit of temperature. The United States uses the Fahrenheit system of temperature units. The metric unit of temperature is Celsius, which is used throughout most of the world. A scientific unit is the Kelvin, used in many heat-related calculations.
Maintain your integrity
Resources
The following resources provide information on this subject:
Websites
Books
Top-rated books on Measuring Temperature
Mini-quiz to check your understanding
1. How did Fahrenheit determine 100° F?
2. Why did Celsius use the freezing and boiling points of pure water to determine his scale?
3. When is 25° K used?
If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.
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Temperature Scales