Laboratory Report #9: Heat and Humidity (Katelyn Kanapi

Laboratory Report #9: Heat and Humidity

(Katelyn Kanapi); (Elle Salud); (Caitlin Sioson)
PHYS 25.02 A

Introduction
Humidity is defined as the amount of water vapor present in the air. The study of humidity is
significant as it is vital in its effects on human health and well-being. The goal of this experiment is to
familiarize the students with the concepts of heat and temperature, humidity, and the use of the heat
index, which combines the two previous concepts. This experiment allowed for the application of
theoretical concepts to real life situations through three sets of activities, which investigated how the
apparent or relative humidity changes with constant temperature, but differing amounts the amount of
water vapor in the atmosphere.
Materials and Methodology
Materials. In the first activity, the experimenters were tasked to make their own thermometer
wherein tap water was poured into the plastic bottle as well as rubbing alcohol. Food colouring was
also added into the mixture. The straw was added to the bottle but did not touch the bottle because the
modeling clay helped it stay in place. For the second activity, the experimenters used cotton wools
where it was secured to the bulb of the thermometer with a rubber band to identify different
temperatures as well. The third activity did not require any materials such that the temperature was
only converted.
Methodology. This experiment was conducted on 21 November, 2018, at SEC C-106A. The
experimenters first started building the thermometer with the help of the materials written above as it
was used to determine the temperature for certain things such as holding the sides of the bottle. The
experimenters then examined the temperature for a wet and dry cotton wool in three different places.
Lastly the temperature taken was converted into Fahrenheit.
Results and Discussions
For the first activity, the experimenters cupped their hands around the bottle filled with water.
The water was seen slowly rising up the straw.

   

For the second activity, the experimenters compared the temperatures recorded by two
thermometers, one with a dry bulb and one with a wet bulb, in three different locations. The
temperatures were recorded in Table 1 and a chart was used to find the relative humidity. For the third
activity, the temperature was converted to Fahrenheit and the heat index chart was studied to
determine possible heat disorders that could arise from prolonged exposure in any of the three
locations

Q2: What is the purpose of adding alcohol in the mixture? Will the experiment work if plain tap water
is used?
Alcohol is needed because alcohol expands more quickly when heated as compared to water
alone. The experiment may not work because water expands slowly and at high temperature at
which one’s hand cannot reach.
Q3: Table in the data sheet.
Q4: Why does the wet bulb thermometer register a lower temperature than the dry bulb thermometer?
The wet bulb thermometer registers a lower temperature than the dry bulb thermometer
because it operates through evaporation. Additionally, evaporation is an endothermic process
which means it absorbs heat and thus having a lower temperature.
Q5: Which has the lowest relative humidity among the three locations? Why? How does the air
conditioner affect the relative humidity in the room?
The air conditioned room has the lowest relative humidity among the three because humidity
makes the environment hotter, and when it is colder then it means there is a low humidity.
Q6: Note from the table that for a given dry-bulb temperature, the relative humidity is higher when the
temperature difference between the wet bulb and dry bulb is small. Why?
The smaller the difference means that the wet bulb’s reading and close to the dry bulb’s
reading. This thus shows how there is a lot of water vapor which does not allow the wet bulb
to evaporate and the relative humidity increases.
Q7: Table in the data sheet.
Q8: What are the possible heat disorders associated with the heat indices that you determined?

1. Room with aircon (71% RH): Fatigue, possible with prolonged exposure and or physical
activity.
2. Open air or outside (79% RH): Sunstroke, heat cramps, or heat exhaustion are possible with
prolonged exposure.
3. Room without aircon (79% RH): Fatigue, possible with prolonged exposure and or physical
activity.
Q9: While in ENgland, where the weather is normally dry, you notice that at 90°F or 32.22°C you feel
cooler than the temperature that is recorded in the thermometer. Here in the Philippines, however, this
temperature can be quite uncomfortable already. Using Figure 1, explain why this is so.
Humidity is higher in the Philippines than in England.
Q10: WIthin what range of values of relative humidity will 90°F (32.22°C) feel cooler than it actually
is, i.e., the apparent temperature < actual temperature.
Humidity must be less than 31%.
Conclusion
The experiment showed how heat and humidity works. The activities effectively deepened the
understanding on why people feel more comfortable with dry air (except if too dry) compared to
moist air where it is extremely humid. Based on an article online by hyperphysics, If the air
temperature is 24 °C (75 °F) and the relative humidity is zero percent, then the air temperature feels
like 21 °C (69 °F).If the relative humidity is 100 percent at the same air temperature, then it feels like
27 °C (80 °F). In other words, if the air is 24 °C (75 °F) and contains saturated water vapor, then the
human body cools itself at the same rate as it would if it were 27 °C (80 °F) and dry.

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