, Research Paper

Biology Coursework Practical Heat Loss

The purpose of this practical is to happen to what extent does the surface country to volume ratio of an object affect the rate of heat loss from the object

Hypothesis: As the ratio of surface country to volume of an object decreases the rate of heat loss from the object will besides diminish. Objects with the same surface country to volume ratios loose heat at the same rate so long as there are non other variables involved.

Background Knowledge:

The surface country to volume ratio of an object is determined by spliting the surface country by the volume and seting it into a ratio of one.

e.g. A flask of volume 200cm3 and a surface country of 160cm2 will hold a surface country to volume ratio of:

160

& # 8212 ; – : 1 = 1.25: 1

200

Objects that are non the same size but have the same surface country to volume ratios loose heat at the same rate. So a flask, with a volume of 200cm3 with a surface country of 160cm2 and a surface country to volume ratio of 1.25:1, will free heat at the same rate as a similar flask of volume 625 and a surface country of 500 which besides has a surface country to volume ratio of 1.25:1. However, by and large when you increase the size of an object the surface country to volume ratio decreases so in this illustration it is really likely that the two flasks in inquiry are different forms.

In this experiment the two flasks which will be used will different come up country to volume ratios as follows:

100 cm3 flask: Volume = 100, Surface Area = 115. Surface Area to Volume Ratio =

115

& # 8212 ; – : 1 = 1.15: 1

100

500 cm3 flask: Volume = 500, Surface country = 330. Surface Area to Volume Ratio =

330

& # 8212 ; – : 1 = 0.66: 1

500

As it is seen the ratio is lower in the 500 cm3 flask. This means that the rate of heat loss should be less than the 100 cm3 flask.

Heat is lost by three different procedures:

* Conduction

* Convection

* Radiation..

Conduction is the procedure by which heat is transferred from on solid to another. When a solid is heated the molecules inside, which are usually about inactive, get down to vibrate. When another solid is brought into contact with the heated solid the energy from the vibrating molecules at the border of the het solid is transferred to the outer molecules of the other solid. This energy so spreads through the 2nd solid until it is besides heated. This procedure is peculiarly effectual in metals.

Convection is the manner by which liquids and gases transfer heat. When gases and liquids heat up they rise and so when air is heated it rises. However as it rises it looses energy to its ice chest milieus. Finally it cools to a point where it begins to fall. Once it is near the beginning of heat it begins to lift once more and takes heat up with it. These rhythms are known as convection currents and it is the manner by which gases and liquids transportation heat. Convection currents become more efficient when they have a larger volume of air so many dielectrics work on the rule of curtailing the motion of air. For illustration pit wall insularity reduces the infinite in which air has to travel and so reduces the efficiency of convection currents.

Radiation is the manner that heat is transferred from a solid to a liquid or gas. It is a mixture of conductivity and convection as, like conductivity, heat is transferred by contact but so it is besides similar convection because the heat pushes the molecules away conveying in colder molecules.

When heat is transferred from one medium to another, as with radiation, there is a grade of inefficiency which consequences with non all the heat being transferred. As in this experiment we will be utilizing H2O in a glass container the consequence of the heat holding to alter from a liquid to a solid to a gas will hold a little consequence on the readings taken nevertheless this likely will non hold a really important consequence.

Method:

For this experiment two flasks will be set up. They will hold volumes of 100 and 500 cm3. These will be attached to a clinch base and so filled with warm H2O. Warm H2O will be used as so less clip will be required to heat the H2O to the coveted temperature of 90oC. One the flasks have been filled they will be heated to acquire the H2O to 90oC. Once the flasks are both at 90oC spiles will be placed in the top which have thermometers running through them. Using these thermometers the temperature will be recorded every 30 seconds for 20 proceedingss. This will so be repeated. The experiment is repeated to better the truth of the informations.

In order to guarantee a just trial the experiment will be started at the same temperature each clip and will besides be allowed to run for the same length of clip. Besides the deepness of the thermometers in each flask will stay changeless for both trials. The volume of H2O will be every bit equal as possible in both experiments nevertheless due to human inaccuracy it is improbable that the volumes will be precisely the same. Hopefully any fluctuations between experiments will be so little as to be of no effect.

At the terminal of the experiment the consequences will be plotted in a tabular array and the mean consequences will be calculated and plotted on a comparative graph so that it is possible to see any fluctuations between the two sets of informations.

Consequences:

Minutess Temp 100cm3 & # 8211 ; 1 Temp 100cm3 & # 8211 ; 2 Temp 500cm3 1 Temp 500cm3 & # 8211 ; 2 Average 100cm3 Average 500cm3

0 90 90 90 90 90 90

1 88 88.5 89.5 88.5 88.25 89

2 86 87 88.5 87.5 86.5 88

3 84.5 85 88 87 84.75 87.5

4 83 84 87 86 83.5 86.5

5 81.5 82 86 85.5 81.75 85.75

6 80 80.5 85.5 84.5 80.25 85

7 78 79 84.5 83.5 78.5 84

8 77 78 84 83 77.5 83.5

9 75.5 76 83 82 75.75 82.5

10 74 75 82 81 74.5 81.5

11 73 74 81.5 80.5 72.5 81

12 72 72.5 81 80 72.25 80.5

13 70 71 80 79 70.5 79.5

14 69.5 70 79.5 78.5 69.5 79

15 68 69 78.5 78 68.5 78.25

16 67 68 78 77 67.5 77.5

17

66 67 77 76 66.5 76.5

18 64.5 65.5 76.5 75.5 65 76

19 64 65 76 75 64.5 75.5

20 63 64 75 74.5 63.5 74.75

Analyzing the Consequences:

These consequences agree with the anticipation that was made. As the graph shows the 100 cm3 flask looses heat much faster than the 500 cm3 flask. So much so that the concluding consequence for the 500 cm3 flack catcher is 11.25oC higher than the concluding consequence for the 100 cm3flask. All four sets of temperature readings, every bit good as the norms, show the same tendency. As clip passes heat is lost at a steady rate. This may non be true for lower temperature readings, nevertheless within the bounds of this experiment it is impossible to foretell any great fluctuation off from the stated tendency. The graphs show just consequences, nevertheless topographic points where mistake occurred are obvious as the graphs gradient alterations because the lessening in rate was less than what was the norm for that flask. Generally for the 100 cm3 flask the lessening in rate was around 1 grade per minute, with some exclusions. For the 500 cm3 flask the rate was by and large 0.5 grades per minute, once more with some exclusions. This is what we expected as the surface country to volume ratio of the 500 cm3 flask is approximately half of the surface country to volume ratio of the 100 cm3 flask. This is shown in the readings that, on the whole, the rate for the 500 cm3 flask was half that of the 100 cm3 flask.

1.15 / 2 = 0.575 Therefore 1.15 / 2 * 0.66

The ground for this is because of two things. In the little flask and the big flask the H2O molecules are traveling at an equal velocity at the start of the experiment. However as clip passes the molecules start to decelerate down. The ground that they don t decelerate down at a faster rate, as they would if they were on their ain, is because all the molecules in the flask are clashing with each other, therefore keeping the impulse. The difference between the little flask and the big flask is that in the big flask there is a greater figure of molecules to clash, this means that the odds of a hit happening are much higher. So although the figure of hits is non plenty to keep the heat, the proportionately higher figure of hits in the higher flask means that the heat decreases at a slower rate as the hits maintain the heat. The 2nd ground for the slower heat loss in the larger flask is that, while the proportionately higher figure of hits in the Centre maintains heat at that place, the figure of molecules hitting the sides is equal. This means that the heat loss from the hits between H2O molecules and the glass of the larger flask is proportionately equal to the little flask. While heat at the margin is lost at the same rate the heat at the Centre goes down at a slower rate and this maintains the heat for longer in the big flask hence the slower rate of heat loss.

There may be other factors such as the different thickness of glass in the two flasks. The big flask has thicker glass as it has to back up more weight. Besides there are other little factors such as the thickness of the spile and exact location of the thermometer. However these are so undistinguished to be of no effect.

Measuring the consequences:

These consequences have shown what we predicted and as they were obtained from a well regulated and controlled experiment we can presume so to be accurate. The consequences do hold some minor defects, nevertheless these are non really serious and do non compromise the truth of the experiment. These little experimental mistakes are, about wholly, human mistakes. Any mistakes that were non caused by human mistake when mensurating are non known to be. If there are any other mistakes apart from human mistake so they are most likely to be unstoppable, for illustration the ambient room temperature which is non governable under the fortunes.

There are ways in which these consequences could be improved or the experiment changed to give better and more utile information. The factors that were wholly out of our control were: the room temperature and the motion of air in the room. The lone manner that these factors could be countered would be in a commercial research lab where the experiment could be conducted under purely controlled environmental conditions. However it is expected that these factors would hold small affect on the overall alteration in temperature. The factors that besides may hold affected the consequences were: the pureness of the H2O ; the truth of the measurement instruments ; the truth of timing and the truth of the volume of H2O. All these factors could be improved upon. Condensing the H2O would take any drosss, which could change the rate that the H2O itself lost heat. By utilizing electronic thermometers and clocking equipment the truth of the readings could be somewhat improved. However it was considered that the readings were likely accurate plenty as they are. The volume could be more accurately measured utilizing a more accurate measurement instrument than the oculus. Equipment such as a pipette or similar could be used to this terminal. Other than this there are no major factors which might necessitate altering.

The experiment could be changed to look into the heat lost from flasks of the same size covered in assorted stuffs. These could be substances like: black pigment ; cling-film ; kitchen foil ; silver pigment ; lard and foam plastic. These provide a broad scope of different dielectric belongingss. The black pigment absorbs and emits more heat radiation because of it colour whereas the froth traps air and so prevents efficient convection currents from being set up. This insulates by a different agencies but could, in rule, be every bit good or better. The lard is suggested because it is close to snivel, it would be interesting to see this as this is the manner that animate beings of course insulate themselves. For illustration animate beings like the seal, seahorse and sea king of beasts all have blubber beds as they live in the north-polar where it is cold. On consideration that would hold to be made with this experiment is the thickness of the insulatory bed.

To reason, the consequences showed the tendency which was predicted at the start of the experiment. Although there were some disagreements these were non serious plenty to be considered as invalid. On the whole the experiment achieved its purposes and proved what was expected.