To convert Celsius reading to Fahrenheit: F = 1.8C + 32 QUESTION: If the temperature increases by 20.0 degrees Celsius, by how much did it increase in degrees Fahrenheit? A. 36.0o B. 68.0o, C. 6.67o, D. 20.0o To convert Celsius reading to Fahrenheit: F = 1.8C + 32 But question deals with change or difference in reading. F1 = 1.8 C1 + 32 F2 = 1.8 C2 + 32 (F2-F1) = 1.8 (C2-C1) F = 1.8 C = 1.8(20.0) = 36.0 If the temperature increases by 20.0 degrees Celsius, by how much did it increase in degrees Fahrenheit? A. 36.0o B. 68.0o, C. 6.67o, D. 20.0o PAUSE CLICK To convert temperature readings from Celsius to Fahrenheit, CLICK we multiply the celsius reading by 1.8 HIGHLIGHT C in “F=1.8C+32” then add 32. HIGHLIGHT 32 “F=1.8C+32” CLICK However, this question deals with a temperature change. The question changes, that the temperature increases HIGHLIGHT “increases” in question by 20.0 degrees Celsius. The conversion formula is different in this case. Let’s see why. Suppose we start with a Celsius reading of C1. The corresponding Fahrenheit reading, F1, is this... Similarly, if we end up with a Celsius reading of C2, the corresponding reading on the Fahrenheit scale is given by F2 in this formula CLICK Now, let’s take the difference: F2 minus F1 equals 1.8 times C2 minus C1. Note that 32 cancels out when you take a difference between two temperature readings. It is customary to represent changes in quantities using the Greek letter delta. CLICK So, we can say that the change in the Fahrenheit reading,... delta F HIGHLIGHT F is simply equal to 1.8 times the change in the celsius reading... HIGHILIGHT 1.8 C When converting temperature changes from celsius to fahrenheit, we multiply the change on the celsius scale but we do not add 32. PLugging in 36.0 degrees for delta C... HIGHLIGHT C and 20.0 we get a change of 36.0 degrees on the Fahrenheit scale. THe correct answer is A. CONTINUED ON NEXT SLIDE

{ } { } C F 104-68 = 36 40-20 = 20 68-32 = 36 20-0 = 20 Confused?.... Here’s another way of looking at this question.... Here’s a figure that shows equivalent readings on the Celsius and Fahrenheit scales. Note that at zero degrees Celsius, the Fahrenheit reading is 32 degrees. HIGHLIGHT At 20 degrees Celsius, the Fahrenheit reading is 68 degrees Fahrenheit. CLICK We can see that the change on the Celsius scale from 0 to 20 degrees is 20. CLICK And the corresponding change on the Fahrenheit scale is 68 minus 32, which is 36. To repeat, a reading of 20 degrees celsius corresponds to a reading of 68 degrees fahrenheit But a change of 20 degrees celsius CLICK corresponds to a change of 36 degrees fahrenheit. Consider a change from 20 degrees to 40 degrees celsius CLICK CLICK This corresponds to a change from 68 degrees to 104 degrees Fahrenheit CLICK and, again, a change of 36 degrees on the Fahrenheit scale. CLICK PAUSE END RECORDING

Video ID: 1A-7-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08