The Factors which Affect Radiation in Small and Large Beakers.

 This will then present me with a comprehensible explanation of the affect of different factors which affect radiation of water through a beaker.

SCIENTIFIC KNOWLEDGE

To enhance my understanding of heat loss and other topics which relate to this topic, I read further to attain some background knowledge, this is shown below:

There are three main ways in which heat can be lost through surroundings; these are conduction, convection and radiation. These are shown below:

CONDUCTION

In metals, the dominant method of conduction is through the movement of electrons. This method of conduction does not operate in non-metals because there are no free electrons (other than graphite). When a metal is heated, the electrons closest to the heat source vibrate more rapidly. Electrons then collide with these atoms and gain more kinetic energy (movement energy). The electrons therefore move around faster and collide with other free electrons which then gain more kinetic energy. Kinetic energy is therefore transferred between the electrons and through the metal from the point closest to the heat source towards points further away. The electrons all travel very short distances but are very fast moving therefore conduction of heat happens very quickly. In metals and in insulators, there is conduction of heat due to the vibration of the atoms. As atoms closest to the heat source absorb heat/thermal energy, they make their neighbouring atoms vibrate more rapidly which then in turn make their neighbouring atoms vibrate more.

EXAMPLES OF CONDUCTION:

• The wire gauzes used on tripods are metal therefore they from revision-notes.co.uk are good heat conductors. Gauzes on cookers are also metal so that heat is conducted quickly and food is cooked fast.
• Poor thermal conductors (insulators) are used for saucepan handles so that they don't heat up and can still be handled.
• Metals are used for the containers which heat liquids e.g. pans, kettles on hobs
• Air is a poor conductor therefore materials that trap air are used for insulation in lofts and hot water cylinders.

CONVECTION:

The cool particles gain kinetic energy when they are heated from the source and expands as it heats up. The particles become less dense than the surrounding cold air therefore it rises and displaces the cool air. Cool particles are more dense therefore they fall and move towards the heat source to take the place of the warm particles. They then heat up and rise while other particles cool down and fall.

EXAMPLES OF CONVECTION:

• Convection is used in fridges to cool it down. Heat is carried away, therefore the back of fridges are always warm.
• Land & sea breezes are due to convection.
• Atmospheric winds.
• Hot water systems.

RADIATION

        The big difference between radiation and convention and conduction is that radiation does not need a medium to travel through; therefore radiation can happen through a vacuum.  Radiation takes place by the transmission of electromagnetic waves (EM waves) from a hot object to any other object. If the rays from a hot object hit another object then some of the rays are reflected and some of the rays are absorbed therefore causing a rise in temperature. The rate as which a body/surface radiates depends on its temperature and the actual nature of the surface. A black surface absorbs more heat than a white surface and therefore radiates more heat. The reason why a white surface radiates less heat is that a white surface reflects all heat and therefore does not retain as much heat hence the inability to radiate as much heat as a black surface.  

EXAMPLES OF RADIATION:

• Heat from the Sun travels to other planets and the rest of the solar system via a vacuum by radiation.
• Grills use radiation to give out heat and thereby cooking food.

VOLUME TO SURFACE AREA RELATIONSHIP

        An organism (or in this case a beaker) that has a large volume in comparison to its surface area (i.e. an elephant) will lose heat less quickly than an organism that has a smaller volume in comparison to its surface area (i.e. a mouse), therefore in theory an elephant loses less heat for its size than a mouse. This is because an organism that has a large surface area compared to its volume will lose heat quicker as it has more surface area to lose the heat and has less heat to lose.  This concept can be used in this investigation to predict and to explain why certain sized beakers lose heat more quickly than others.

PREDICTION

        With reference to my theory, I predict that the small beaker will lose heat via radiation the fastest and I also predict that largest beaker will lose heat the slowest. This is because the small beaker as a small volume to surface area ratio meaning it has more surface area to lose heat and it has less heat to lose hence greatest heat loss (through radiation). The large beaker, however, will lose heat (via radiation) at a slower rate because it a large surface area to volume ratio meaning it has a less surface area to lose heat and it has more heat to lose. I also predict that the beakers that have a insulation to reduce radiation will lose heat more slowly. More specifically, the beaker that will have a black insulation will lose heat more quickly than the beaker that will have a white insulation. This is because black surfaces absorb more heat and therefore radiate more heat and white surface reflect more heat hence radiate little heat.  

METHOD

1. Firstly, I got all the apparatus that were needed.
2. I placed some bubble wrap on the workbench and placed the beakers on top of it.
3. I boiled the water in the kettle and then carefully poured it in the beaker to the right amount that was needed for the experiment.
4. Foil was then used to cover the top of the beaker. Using a scalpel a small hole was cut for the thermometer to be placed in the beaker.
5. An insulating material (wither white or black bag) was wrapped around the beaker to reduce radiation.
6. The temperature started to drop and at a certain temperature (which would remain constant throughout each of the experiments) the stop clock was started.
7. Each experiment lasted one hour and every 12 minutes for an hour the temperature readings were taken (therefore five readings in total).
8. The same method was used for each of the other experiment.

APPARATUS

        

        In this experiment the following apparatus were used:

• Kettle – to boil the water
• 2x 175ml beakers
• 2x 125ml beakers
• Thermometer – to measure the temperature of the water.
• Foil – placed on top of beaker (as a lid) to stop convection.
• Bubble Wrap – placed on the bottom of the beaker to stop conduction.
• Stop clock – to measure the time for the experiment (and time to take readings at).  
• Foil – used on top of the beaker (as lid) to stop convection.
• Bubble Wrap – placed beneath beaker to strop conduction.

         In order to investigate the factors which affect radiation, I must stop/reduce to a possible minimal conduction and convection in the beakers. After thorough research it was found out that a very good and practical way of stopping conduction was to use bubble wrap and to stop convection use foil on top of the beaker. Foil was used because it has a silver surface therefore it won’t absorb heat and will just reflect all the heat back into the beaker – therefore heat it maintained at not lost through convection. . Bubble wrap was used because it has air pockets. The air is a very good insulator, so won’t conduct the heat. This retains the heat in the beak and so no heat is lost via conduction.

DIAGRAM OF EXPERIMENT

SAFETY

Generally, this experiment was straightforward to conduct. There were some aspects of the experiment that I had to be very careful with, to ensure that my or anyone else’s safety was not put at risk. In this experiment the main aspects I will have to be very careful with glassware and the boiling water. When I conduct the experiment, I will wear safety goggles so that no harmful substances (i.e. the hot water) can get in my eyes. I will wipe down my own workbench when the experiment is over, so that no hot water will be left therefore reducing the chance for anyone to be burned. I will also take extra precaution when handling the glass beakers.

FAIR TEST

I will have to ensure that I keep this experiment a fair test. If I fail to do so, then I will obtain the wrong results as they are unfair which will then give the wrong conclusion.

        Initially, I will have to ensure that the initial temperature of the beakers is the same in all experiments. I have to ensure that conduction and convection are stopped with the same insulating material each time. The same type of thermometer will be used in each experiment, i.e. a mercury thermometer. This will eliminate the chance of any variations in the readings and so the readings will be consistent in terms of their accuracy and reliability.   

                I will conduct all experiments at room temperature, so that I do not obtain the wrong results. I will allow one hour for all of the experiments and the readings will be taken every 12 minutes.  If I fail to do this then the results that I will obtain will be inaccurate as the experiment is unfair.    

VARIABLES

        To ensure that my experiment is a fair test, I must consider certain elements of my experiment to vary and others not to. In this case, I am going to vary the size of the beaker and the insulating material. The  time scale for all experiment that is allocated is one hour with 12 minute readings each time (in minutes) – 0m, 12m, 24m, 36m, 48m and 60m. I have chosen this range because it will provide me with wide and adequate results on which I can develop a sufficient conclusion. If none of the non-variables are kept constant, it would mean that this experiment would not be a fair test consequently leading to the wrong conclusion. The aspects of the experiment I will be varying and leaving constant are listed below:

• Varying the type of the insulating material to stop radiation (i.e. black bag and white bag)
• Varying the size of the beaker (125ml beaker and 175ml beaker).
• The time will be the same for each experiment.
• The material stopping conduction (bubble wrap) and convection (foil) will used in all experiments.
• The initial temperature of the beaker will be the same.

PRELIMINARY WORK

I carried out the same the same experiments as my preliminairy experiment. I did this because it provided me with an adequate perception of the results that I was going to obtain from my actual experiment. Therefore, from this I had a sufficient concept on how to carry the experiment out more accurately. The results I gathered from my preliminary experiment are shown below:

EXPERIMENT                                                        CONTROL

        In this experiment, a smaller time scale was used than in the main experiments. This is because I only wanted to test my prediction to see if it was right and to gain an insight into the results that were going to be gained.

        The results that as time went on the temperature of the water in the beakers of both experiments went down. The temperature of the control beaker decreased more significantly than the temperature in the experimental beaker. This is because the control did not have any cover to stop radiation.  The graph on the following page shows the trend more clearly. The graph shows that time and temperature (temperature loss) have an inverse relationship because as time increases the temperature decreases.

Modification of Preliminary Experiment to Main Experiment

When carrying out the preliminary experiment, there were some flaws in the experiment that were noticed. The main flaws (and the only ones) in the preliminary experiment was that the volume of water in the experimental beaker and the control beaker were different. The initial temperature of the experimental beaker and control were different. The other fault in the preliminary experiment was that both experiments were started at different times.

In order to gain sufficient and consistent results these flaws in the preliminary experiments were rectified in the main experiment.