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Before giving you an injection, a physician swabs your arm

University Physics | 13th Edition | ISBN: 9780321675460 | Authors: Hugh D. Young, Roger A. Freedman ISBN: 9780321675460 31

Solution for problem 18DQ Chapter 17

University Physics | 13th Edition

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University Physics | 13th Edition | ISBN: 9780321675460 | Authors: Hugh D. Young, Roger A. Freedman

University Physics | 13th Edition

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Problem 18DQ

Before giving you an injection, a physician swabs your arm with isopropyl alcohol at room temperature. Why does this make your arm feel cold? (?Hint: The reason is not the fear of the injection! The boiling point of isopropyl alcohol is 82.4o C.)

Step-by-Step Solution:

Solution 18DQ Step 1 of 2: The reason for this is latent heat of evaporation. That is, when liquid evaporates it absorbs some certain amount of heat energy from surrounding to go from liquid to gaseous state. That energy is released when gas condenses back to liquid. Similarly as isopropyl alcohol has lower boiling point(temperature at which liquid changes as gas) and is rather volatile; that is, even at room temperature it will evaporate quickly. This evaporation requires energy, and the result is that while alcohol is evaporating, it absorbs heat (and thus feels cold) from both the skin underneath it and also from the air around it. Thus skin feels cool as the alcohol evaporates away.

Step 2 of 2

Chapter 17, Problem 18DQ is Solved
Textbook: University Physics
Edition: 13
Author: Hugh D. Young, Roger A. Freedman
ISBN: 9780321675460

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Before giving you an injection, a physician swabs your arm

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