Gentiana Spahiu
There are multiple ways for students to learn theories, techniques and other information
they would eventually need in their lives and I believe that the best way of teaching is
through demonstration and student activities. The chapter of Lab experiments continues
with yet another demonstration of things we know just because we are told of them. And
yet again we have the chance to actually perform and witness different dynamics of
substances, events, and chains of actions and reactions.
The Lab on Thermal Heating would inform us on the amount of energy absorbed by various
liquids with different characteristics when heat is involved.
For this experiment we were provided with two 100 ml beakers where one contained 80
ml of water and the other carried 80 ml of vegetable oil, both of room temperature. We
were also given a hot plate (something similar to what they used to cook a while back) and
two temperature probes. Last but definitely not the least, we were provided with access to
our constant companions of these labs: NXT Motor and LabView application. To conduct
the experiment the professor pointed out the famous formula of the day would be:
ΔE=m c Δ
ΔT
where :
Δ E: Amount of energy absorbed (J)
m: mass of a liquid (g)
c: Heat capacity: (J/g-K)
ΔT : change in temperature (K)
: mass density (g/ml)
Looking at the formula and at the experiment instructions we realized that some prep work
was needed. First we plugged the hot plate and set it to 1.5 to warm up. Then the formula
required that we researched the internet to find the heat capacity (c) and mass density (r)
of both water and oil.
GOOD TO KNOW:
- Heat capacity or Thermal Capacity: the measurable physical quantity that characterizes
the amount of heat required to change a body's temperature by a given amount. It is usually
measured in Joules per Kelvin.
- Mass Density: material's mass per unit volume.
So, we found:
Coil = 2 J/K
C water = 4.184 J/K
 oil = .92
 water= 1
On with the Experiment......
WATER
22.351101
22.351101
22.351101
22.250099
22.250099
22.250099
22.351101
22.351101
22.452049
22.552971
22.65386
22.85552
ΔT= 0.504419
OIL
20.32272
20.22076
20.22076
20.22076
20.42462
20.628241
20.83165
20.933281
21.23786
21.339279
21.64328
21.74452
ΔT=
1.4218
Once the hot plate was warmed enough we placed the two
beakers of liquids on it and inserted a temperature probe in
each of them without touching the glass walls. We then ran
the LabView application for a preset time of two minutes to
gather the temperature changes in the liquids and record
them on an Excel Sheet.
The findings were as follows:
Interestingly, when looking at
the table we see that the water
starts off with slightly a higher
temperature than the oil, but as
both liquids are warming up and the temperatures are increasing I noticed that Oil was
warming up more than water (as expected). When the two minutes were up, the water still
had a higher temperature but in terms of temperature oil had absorbed more heat. I found
that many were confused on why the water had a higher temperature at the end and I
guess we can attribute that to the fact that water initially had a higher temperature to start
with. Meanwhile we need to pay attention to the change of temperature in both liquids. In
our experiment such change was (initial temp- ending temp.):
ΔTwater= 0.504419
ΔToil= 1.4218
Clearly the oil's temperature changed the most. Now that we have all the elements needed
to plug in the formula we can calculate the energy absorbed by both liquids:
ΔE water= 168.84 J
ΔE oil= 209.29 J
We were then required to calculate the percent error for the experiment and possible the
source of it. To compute the error percentage we used the formula:
ΔE water- ΔE oil|/Average(ΔE water, ΔE oil) 100% = 21.4%
The result of 21.4% I thought it was relatively decent considering the human error in
conducting the experiment. Other reasons why such error occurred could be the fact that
the initial temperatures of the liquids were different (very relevant), the problem our
group had with heating up the hot plate and moving the beakers around before we finally
inserted the temperature probes (to emphasize here- We never let the probes touch the
glass walls).
Conclusion:
As expected the oil heat up faster than the water and this is due to the different
characteristics that materials and liquids have. Such knowledge helps people to better
define the kind of materials they would use for different projects. A person who is thinking
of building a house will certainly consider the different building materials (wood, bricks, or
glass) not only in terms of cost but even in terms of heat absorption and retention.