CALORIMETER

execution of the esperiment

EXECUTION

When we dipp an object, called C (at temperature Tc), in water (at temperature Ta < Tc), the heat pass on the water from the object, until the two temperatures become the same (te). In absence of heat dispersion, the amount of Q lost from C, is absorbed from the water and from the bodies with which it is to contact. Just in order to hold account of the heat absorbed from these objects, it is necessary to execute a measure associating to the calorimeter a water mass me: called equivalent in water (illustrated in the previous paragraph). After all the specific heat will be given from the relation:

where tf is the initial temperature , te that final, tc the temperature of the champion, mc its mass and ma the water present inside the instrument.
We used a stove to warm the object and raise the temperature of the object, hotter than the water inside of the calorimeter.
Dipping it to the inside of a container already filled up with water and placed on a stove, at the moment of the boiling the temperature of the champion will be approximately 100°C. Holding account of the "way" that it will cover, from the stove to the inside of the calorimeter, during which it will yield heat to the atmosphere, we considered tc 97°C. With a balance we determined the mass mc of the champion.

We placed in the vase of Dewar a mass of water, measured with a graded cylinder; in this case the instrument possesses a maximum capacity of 50cc; in order to catch 150cc (or grams) of water to pour in the calorimeter will be necessary three measures that they will increase the associated error to the measure; being the sensibility of the graded scale on the cylinder of 0,1cc it's opportune to associate an equal uncertainty to 0,3cc.
We dipped the thermometer and the mixer through the cover. Now the temperature stabilized itself, tf = 20,2°C. we extraced the object, at temperature tc, from the stove and we introduced more quickly possible inside the water on the vase.
The body must be on the water without to touch the walls of the vase, or the instruments.
So calling the temperature of the water inside the calorimeter tf, this will go upper because of the exchange of heat with the body. It will be necessary periodically to mix the water in order to make the temperature uniform.
We called the temperature stabilized te. But the value to consider it is the "central value". The theoric data of the temperature of equilibrium would not coincide with the "central point" experimentally, but with a value a little more elevated. If the intermediate temperatures to always equal distances of time are recorded and defined with a manual chronometer, it will be possible draw a graphic (you see to side) where the course of the temperature will describe a curve.
If we draw two tangents to this curve it's possible to find their point of encounter, that exactly corresponds to a value a little more elevated than that one found during the experiment. Obviously this data is preciser because it does not hold account of all the heat dispersions.

DATA AND CALCULATE

ma (g)	me (g)	mc (g)	tf (°C)	tc (°C)	te (°C)
150	5	14,7	20,2	97	21,7

In this case we considere te 21.7°C, to which will be associated the semisensibility of the instrument that is 0.05°C. Instead we considered the mass uncertainty of 0.1g.
Usually the specific heat is calculated in Kelvin; but our values are indicated in Celsius degrees; the interval of a degree is equal in both the scales, so we didn't translate such data from an unit of measure to the other.
We obtain the specific heat of the object

The relative error to this measure can be calculated with the next expression:

Therefore the uncertainty associated to the specific heat will be:

The final result therefore is:

Through this result we can understand the metal of which the solid used in the experiment is constituted, that is the aluminum (cs=0.215 cal/g.K).
If we use the ideal value of te found in the graphic, 21,735 °C, is possibie to obtain an exact result:

CONCLUSIONS

execution

data and calculate

conclusions

There are much subtle factors to be considered:

The champion can touch the walls or the instruments in the vase of Dewar, indeed the glass of the thermometer and the axis of the agitator absorb heat.
If we used the mixer with much violence some water could remain on the walls or on the cover of the calorimeter; moreover our force, that is a mechanical energy, becomes thermal, so increase the temperature.
A small part of water could evaporate.
Like previously said, the champion disperses heat with the atmosphere when he comes from the stove to the calorimeter, so we considered tc 97°C.
The calorimeter must have a shape that limited, if it's possible, the dispersion of heat, therefore vase of Dewar is a cylinder not a container lengthened or extended horizontally.
Some water remain attack to the walls of the graded cylinder.
In the reading of the level of water, to the inside of the graded cylinder, or mercury, in the thermometer, and the intervals of time on the chronometer, the observer can have store clerk parallax error.
The recording of the intermediate temperatures demands two executory: one controls the intervals of time with the chronometer and an other that record the temperatures; obviously the times of reaction between the observer with the chronometer and the reader of the thermometer cannot be neglected.
The measure of the mercury or of the water in the cylinder, isn't correct because the "meniscus" formed on both the substances (in the first convex and in the other concave). This phenomenon happens in virtue of the prevalence of the adhesion forces on those of cohesion (look at the fig.).