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Dr. Walt Volland revised July 11, 2012 all rights reserved
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The three most common temperature scales are Fahrenheit, Celsius and Kelvin. The illustration below shows identical liquid filled thermometers. Each is calibrated with one of the three temperature scales. The Fahrenheit and Celsius scales show the boiling point for water at 212oF and 100oC. The freezing point for water is 32oF and 0oC. The size of the degrees is different. In the Fahrenheit scale there are 180 degrees between 32oF and 212oF. while in the Celsius scale there are only 100 degrees between the water frezzing point and boiling point. The Fahrenheit degrees are smaller, so there are 1.8 times as many of them. These temperatures are definitions so they are exact numbers. Click here for more about degrees F or click here for history behind Fahrenheit scale The Celsius and Kelvin scales have the same size degree, but have different 'zero' or starting points. The freezing point for water is 0oC and 273.15 in the Kelvin scale. Conversions between the Kelvin and Celsius require the addition or subtraction of 273.15. This makes conversions simpler. click to access unit converter site
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EXAMPLE What is the Kelvin temperature for a room with a Celsius temperature of -11oC? SOLUTION To figure the Kelvin temperature from Celsius add 273.15 to the Celsius temperature. Kelvin = Celsius + 273.15; Kelvin = -11 + 273.15 = 262.15 Kelvin The answer should be rounded to 262 Kelvin with no digits past the decimal point beause the -11 had none and is the least reliable number. EXAMPLE What is 98.6oF in the Celsius scale? SOLUTION To figure Celsius we use this relationship. C = (5/9)( F - 32) . Celsius = (100 degrees C / 180 degrees F) ( F - 32) = (5/9)( F - 32) We convert Fahrenheit to Celsius by subtracting the extra 32 at the freezing point for water from the Fahrenheit value and then multiply by 5/9 to convert the small Fahrenheit degrees to the bigger Celsius ones.click access converter page Celsius = (100 degrees C / 180 degrees F) ( 98.6oF - 32) Celsius = (100/180)( 98.6oF - 32) = (5/9) ( 98.6oF - 32 ) Celsius = (100/180)( 66.2oF) = 37oC EXAMPLE What is -49oC in the Fahrenheit scale? SOLUTION To figure Fahrenheit we use this relationship. F = (9/5) C + 32. Fahrenheit = (180 degrees F / 100 degrees C) ( Celsius) + 32 = (9/5) C + 32oF We convert Celsius to Fahrenheit by multipling the Celsius value by 9/5 to convert the big Celsius degrees to the smaller Fahrenheit ones. Then we add 32 to account for the difference in the freezing point for water in the two scales. Fahrenheit = (9/5) ( - 49. oC ) + 32oF Fahrenheit = (9/5)( - 49. oC) + 32oF = - 88.2o + 32oF = - 56.2 oF Fahrenheit = - 56.2 oF |
