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Homework Help: Temperature conversion

  1. Jun 19, 2007 #1
    1. The problem statement, all variables and given/known data

    On the moon the surface temperature ranges from 371 K during the day to 1.09 102 K at night.
    (a) What are these temperatures on the Celsius scale?
    (b) What are these temperatures on the Fahrenheit scale?

    2. Relevant equations
    T=Tc+273.15 T=Kelvin temperature Tc=Celcius
    9/5 F degrees/(1 C)

    3. The attempt at a solution

    I got both answers right for part a but for part b the answer solution says that my answers are incorrect.

    What I did was first plugged in each temperature given in the problem separately into the equation to find celcius. I ended up with 97.85 C and -164.15 C which were correct! Then I used the second conversion 9/5 F degrees/(1 C) to find each of the temperature for farenheight using the celcius degrees answers from part a I got 176.13 degrees F and -295.15.
    I think I worked this out correctly but the key says I'm wrong
     
  2. jcsd
  3. Jun 19, 2007 #2

    berkeman

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    There's an offset in the F temperature scale. Water freezes at 0C, but not at 0F. Does that help?
     
  4. Jun 19, 2007 #3

    cepheid

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    You're forgetting that the zero points of the Fahrenheit and Celsius scales are not the same. More specifically, 0 degrees C is equal to 32 degrees F. As a result, you have to shift. I'll leave to you to determine whether to shift, then convert, or whether to convert, and then shift.
     
  5. Jun 19, 2007 #4
    Oops

    So I need to subtract 32 degrees from each answer to take an account for the freezing pt.
     
  6. Jun 19, 2007 #5

    cepheid

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    Not quite.

    97.85 C means 97.85 Celsius degrees above freezing. When you convert these to Fahrenheit degrees, it means 176.13 Fahrenheit degrees above freezing, where freezing is 32 F. So...
     
  7. Jun 19, 2007 #6
    first i would take the celcius and subtract 32 degrees since its above the farenheight freezing pt. and then convert to farenheight by multiplying by (9/5)....right....and in the other part i would add 32 degrees since its below the zero pt??
     
  8. Jun 19, 2007 #7

    chemisttree

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    Both scales are equivalent at -40 degrees. Start from there and use the ratio you know. Be sure to readjust your answer to account for the 40 degrees.
     
  9. Jun 19, 2007 #8

    cepheid

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    No and no. The conversion algorithm is always the same, and you have got it wrong. Think about it this way: How would you convert 0C to Fahrenheit?

    EDIT: By the way, I was hoping you'd complete the thought here, that was the point of my post:

     
    Last edited: Jun 19, 2007
  10. Jun 19, 2007 #9
    Man I was making this problem much tougher than it was! thanks for your help!
     
  11. Jun 19, 2007 #10
    o sorry, When you convert these to Fahrenheit degrees, it means 176.13 Fahrenheit degrees above freezing, where freezing is 32 F. so, Tf = (9/5)*Tc+32
     
  12. Jun 19, 2007 #11

    cepheid

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    This is the exact point I was getting at, and the equation you posted above is the correct conversion formula! I'm glad you arrived at it by reasoning it out, that's what I was hoping to coax you to do! :smile:
     
  13. Jun 19, 2007 #12
    sometimes i just try to complicate problems...thanks for your help I appreciate it very much ;-)
     
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