Chapter 23, Problem 20A

Why is it important that a finger be wet before it is touched to a hot clothes iron?

To determine

To find the importance of a finger to be wet before it is touched to a hot clothes iron.

Answer to Problem 20A

The finger to be wet to safeguard it from burning.

Explanation of Solution

Introduction:

When two objects at different temperature comes in contact, heat is transferred from hotter object to colder object. When the colder object is wet, certain amount of transferred heat is used to evaporate the water on the wet object and only the remaining heat reaches the object.

When the wet finger touches the hot clothes iron, heat is transferred from iron to finger .Some portion of this heat is used to evaporate the water layer on the finger .Only remaining heat is transferred to our finger. Since the specific heat and latent heat of vaporization of water is large enough, this portion of heat used to evaporate water is larger than the heat transferred to our finger. Thus, we can avoid burning of our finger.

Conclusion:

Thus if the finger is wet when it touches the clothes iron, finger will be safeguarded from burning.