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Homework Help: Unit Conversion

  1. Nov 15, 2014 #1
    1. The problem statement, all variables and given/known data
    A Celsius and a Fahrenheit thermometer are dipped in boiling water. The temperature of the water is brought down until the Fahrenheit thermometer reads 140°. So, the fall in temperature registered by Celsius scale is:

    2. Relevant equations

    3. The attempt at a solution
    Boiling water is 212 F. 212-140=72.
    Convert 72 F to C and I get 22.223 C.
    My answer doesn't match any of the choices.
  2. jcsd
  3. Nov 15, 2014 #2


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    Homework Helper

    If F=1.8C+32

    Then F1=1.8C1+32
    and F2=1.8C2+32

    So you change in F, F2-F1= ? (write in terms of the formula and you'll see that the change in F can't be converted to C using the standard formula).

    Alternatively, convert everything to C first.
  4. Nov 15, 2014 #3
    Got it. Thanks a lot!
  5. Nov 15, 2014 #4


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    Staff Emeritus
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    Homework Helper

    The reason '32' appears in these temperature conversion formulas is that in the Celsius scale, water freezes at 0 C, while this occurs at 32 F on the Fahrenheit scale. Between freezing and boiling, there are 180 Fahrenheit degrees and 100 Celsius degrees, so each Celsius degree is 180/100, or 9/5 Fahrenheit degrees.
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