Physics Group 4 Project Essay, Research Paper

Physics Group 4

Project ??????????? After being

set our initial topic of the bath tub, we chose as a group to investigate the

heat lost from a bath tub.? We initially

experimented with ideas such as using different shapes, sizes and materials.? Eventually, we decided that the easiest

option was to investigate how the thickness of a bath tub effects the heat

loss, as well as how conduction, convection (evaporation) and radiation

effected the heat lost from a bath tub and how we could reduce these forms of

heat loss. We chose to use vacuum formed plastic bath tubs as they were the

quickest to build, and we did not want to waste valuble experimenting time

building lots of bath tubs.? The

polyethene plastic also mimicked the material of a real bath tub fairly

successfully.The investigation of energy (heat) lost in different bath

tubs. ??????????? We began

our investigation by determining the specific heat capacity of water. In order

to do this, we took a known mass of water in an insulated beaker and gave it a

known quantity of energy by using an emersion heater.? We also used an accurate thermometer in order to take the

temperature change in the water.? We

then used the equation: ??????????? E = mc∆t We then rearranged the formula to give: ??????????? c = E/m∆t In order to calculate the specific heat capacity of water

(c), we took the known quantities of mass, energy and the change in temperature

and inserted them into the above equation. In order to calculate the energy

given to the water, we used electricity to heat the water, by doing this we

were able to calculate the energy using P = VI.? We measured both the voltage and the current that we used to heat

the water.? We had previously weighed

the water and hence we knew the mass, and the change in temperature we measured

using a thermometer.? Hence we were able

to calculate the following values for the specific heat capacity of water: Test 1 Test 2 Test 3 Average Specific heat capacity of water 4745 4723 4216 4561 ??????????? The actual

specific heat capacity of water is 4200.?

We would expect our results to be lower than this value.? However, the beaker was very well insulated

with a lid and hence little heat would have been lost to the surroundings.? The high values can be explained due to: –

The inaccuracy of the probe thermometer we used.? We later found it was not the most accurate

thermometer available to us.? For the

remainder of our experiments we used a far better digital probe type

thermometer. –

The inaccuracy of the digital ammeters, voltmeters and the

unreliability of the power pack and the immersion heater. –

The impurities in the water which was not deionised.Background to our experiment ??????????? We

researched the different methods of heat loss and came up with the following

information: Conduction: The mechanism by which heat energy is

transferred through solid materials. In the case of our experiment, the heat

from the water will be transferred to a certain extent through the plastic

walls of the bath tub by conduction. Evaporation: The mechanism by which most energetic molecules

escape from the water surface leaving the less energetic molecules behind.? This means the internal energy of the water

is then lowered and its temperature is decreased. Convection: The mechanism by which fluid ?currents?, caused

by the differential densities of hot and cold fluids, move.? As the fluid gets ?hot? the particles

vibrate more, and therefore expand, become less dense and rise.? These particles then cool, become less dense

and sink. For the purpose of this experiment, I will consider the heat

lost by evaporation and conduction as one and the same thing as they are nearly

impossible to separate in a liquid such as water. Radiation: The mechanism by which energy from the water is

lost to the surroundings by electromagnetic waves.? This occurs even at low temperatures.? The Investigation ??????????? We began

our experiment by building two vacuum formed bath tubs of different

thicknesses.? We decided that in order

to investigate the effect of thickness as well as the heat loss from

conduction, convection and radiation we would undertake the following

experiments. 1)

We would fill both bath tubs with 700g of water and heat them

up to approximately 42.5 degrees, the temperature of an average bath tub.? We would then measure the heat lost from

both the thick and thin bath tubs in a 45 minute period.? We will record the change in temperature

every five minutes and from this hopefully plot a heat loss curve. 2)

We will then put a lid on the bath tubs to reduce the heat

loss due to evaporation and repeat the same experiment. 3)

We will then put insulation around the bath tubs to reduce the

heat loss due to conduction and repeat the same experiment. 4)

We will the paint the bath tubs silver to reduce the heat loss

due to radiation and repeat the same experiment. From these experiments we hope to

be able to calculate the heat loss due to conduction, convection and radiation

by virtually eliminating each of these forms of heat loss in turn and thereby

calculating? how much is lost through

each of these forms of heat loss. ????? We

wanted to make our measurements of heat loss as accurate as possible.? After our initial experience with the

inaccuracy of the probe we used for our heat capacity of water experiment we

wanted to have a more accurate thermometer. We experimented with a thermocouple

but the galvanometer was too sensitive for our purposes.? We therefore used a more accurate digital

probe and calibrated it before each experiment in order to calculate the error

in our readings.Experiment 1: ????? In

this experiment I used two vacuum formed bath tubs of differing thicknesses. Results: Time

(mins) Heat Lost

(’C) Heat Lost

(’C) 5 1.6 2.7 10 1.5 1.7 15 1.2 1.3 20 1.1 1.1 25 1 1.3 30 0.8 0.7 35 0.8 0.8 40 0.7 0.7 45 0.7 0.6 Total

Heat Lost 9.4 10.9 I have drawn two graphs of these

results to show the heat loss curve by plotting the heat lost against time for

both the thick and thin bath tubs.Experiment 2: ????? In

this experiment I used two vacuum formed bath tubs of differing thicknesses

with lids on them. Results: Time

(mins) Heat Lost

(’C) Heat Lost

(’C) 5 2 2.3 10 1.2 1.2 15 1 0.9 20 0.8 0.8 25 0.7 0.8 30 0.6 0.6 35 0.6 0.6 40 0.6 0.5 45 0.5 0.4 Total

Heat Lost 8 8.1 Experiment 3: In this

experiment I used two vacuum formed bath tubs of differing thicknesses

surrounded by insulation. Results: Time

(mins) Heat Lost

(’C) Heat Lost

(’C) 5 1.7 1.9 10 1.2 1.3 15 1 1.1 20 0.9 1 25 0.8 0.9 30 0.8 0.9 35 0.7 0.9 40 0.6 0.8 45 0.2 0.7 Total

Heat Lost 7.9 9.5 Experiment 4: In this experiment

I used two vacuum formed bath tubs of differing thicknesses painted silver. Results: Time

(mins) Heat Lost

(’C) Heat Lost

(’C) 5 2.2 2.3 10 1.3 1.5 15 1.4 1.4 20 1.1 1.3 25 1 1.1 30 0.8 0.9 35 0.8 0.9 40 0.8 0.8 45 0.5 0.7 Total

Heat Lost 9.9 10.9 Graph of the Total Heat

LostConclusions to be drawn

from our graph: ·

The lid and the surrounding insulation had a

significant impact on the heat lost from the bath tub. ·

Painting the bath tubs silver had no real impact ·

The thick bath tub lost more heat than the thin one. ·

The silver painted bath tub lost more heat than the

normal bath tub. ·

Heat loss was not uniform but varied.Conclusion: ??????????? As the

insulation and lid on the bath tub made a significant difference to the heat

lost from the bath tub, we assumed initially that the heat lost through

conduction and evaporation had been significantly reduced by the insulation and

the lid respectively.? However, on

further investigation we found that plastic is such a poor conductor that it is

unlikely that any heat was lost was lost through this method and it is more

likely that the heat that we initially assumed was lost through conduction was

lost through radiation.? We can

therefore assume that the greatest amount of heat is lost through evaporation

and some was lost through radiation, in comparison the heat lost through

conduction was minute.? The thickness of

the bath tub also makes a difference, as the thicker the bath tub is, the greater

the insulation, the greater the reduction of radiation.? The silver painting did not make much

difference as although some heat was reflected by it, the bath tubs were so

thin that most of the heat escaped and in comparison, the heat reflected back

by the silver was almost immeasurable. ??????????? The results

of our experiment showed conclusively that most of the heat was lost through

evaporation, radiation also had a significant effect as when the bath was

insulated the heat loss was reduced significantly. We can therefore conclude

that the best bath tub would be one that was insulated and with a lid on it.Evaluation: ??????????? Our results

were, on the whole, fairly accurate, however, we did encounter some

difficulties.? Firstly, the temperature

probes we used were extremely unreliable, despite calibrating them for errors,

it would take at least 30 seconds for them to settle down and reach the right

temperature and therefore it is likely that during the 30 seconds the

temperature would have dropped considerably and hence making our results

slightly in accurate.? In order to

irradicate this, if I was to repeat the experiment I would use a computerised

temperature measuring device. This would enable me to accurately plot a graph

as the computer could be programmed to take the results at far more regular

intervals far more accurately.?

Secondly, our methods of eliminating heat loss were not entirely

reliable.? In each case it is likely

that despite our best efforts to reduce heat loss, our insulation was not 100%

reliable.? The worst of all our attempts

to reduce heat loss was the bath tub we painted silver as the silver paint

actually melted the thin bath tub making the plastic thinner and thus

increasing the heat loss, hence the inconsistencies in the graph above.? If repeating the experiment I would be

careful to use thicker plastic and less silver paint.? Furthermore, despite good results, I felt the 1mm difference in

the thickness of the two bath tubs was insufficient to give a real indication

of the effect of thickness on heat loss.?

In a future experiment, I would use far thicker plastic to differentiate

between the two.? Other problems were

encountered with our poor fitting insulated lids which could have been

improved. ??????????? Despite our

problems, I feel that our experiment has been a success, we worked together well

as a group and our results on the whole were valid.? Although our experiment could have been improved, and in

conducting a future experiment, I would make amendments to the temperature

measuring equipment particularly, through the experiment, I feel our

experimental technique improved and the experience of doing a longer experiment

was extremely useful.