Category Archives: Questions

Ask questions in this space and the instructors will answer them.

Quiz grading question

A student asked: Professor, Just a quick question. When grading the quizzes. Do you take the average of the two scores for the quiz and this is my grade? Or do you take the highest score on the quiz, and that is the grade? Thanks
My answer:   Thank you for your question.  We take the best of the 2 scores.

Question about Fahrenheit vs Kelvin

A student asked:

Prof. Roe,

I was reading through the 1.1 notes and copyed down the algebraic formulas for converting between Celsius, Fahrenheit, and Kelvin. The Fahrenheit to Kelvin conversion, middle/bottom of the table, confuses me. It says K = 5/9F + 255. I get the 5/9F to convert it to celsius, keeping in mind that the -32 degrees would come off from the 273. I get 241 when I subtract 32 from 273, rather than 255. Am I confused or is this a typo?

 

My answer: Great question!  To see what is going on here, look at the more familiar formulas

\[ C = {\frac59}(F-32), \quad K = C + 273 \]

which are also found in the table you mentioned.  Putting these together gives \(K = {\frac59}(F-32) + 273\).  Now you must use the distributive law  to write

\[ K = {\frac59}(F-32) + 273 = {\frac59}F – {\frac59}\cdot 32 + 273 \approx {\frac59}F – 18 + 273 = {\frac59}F + 255 , \]

because \(\frac59\) of 32 is approximately 18.  Hope this helps.