My aim is to investigate the rate of energy loss in different types of cups by thermal radiation. Def: Radiation is a process when heat is sent from one place to another, by waves, without heating the space in between. Def: Conduction is when energy is passed from one vibrating atom to the next. Def: Convection is what happens when hot liquids and gases expand and rise while the cool liquid or gas falls (a convection current).
Apparatus list: 3 polystyrene cups –> one painted black (matt)–> one plain white (matt) –> one covered with aluminium foil (shiny) hot water – caution! (3x 70ml) cold water (3x 70ml) a graduated measuring cylinder a thermometer a pen a heatproof mat (for safety: HOT WATER! ) polystyrene lids – with holes in middle to insert thermometer (x3) a stop-clock/watch Prediction: Dull, dark surfaces are good radiators (i. e. lose heat/energy more easily), but bright, shiny surfaces are poor radiators (i. e.store heat/energy more easily).
Therefore, part of my prediction is that the painted black matt polystyrene cup will lose the most heat or energy, as it is matt (dull) and black (dark); the polystyrene cup covered in aluminium foil will keep the most heat because it is silver (bright) and made of foil (shiny); whilst the plain white polystyrene cup will lose some heat, as it is matt (dull) but at the same time, it will be able to store some heat as well as it is white (bright).
Metals are good conductors so the aluminium foil will help conduct heat, however, liquids are poor conductors (i. e. they lose heat quickly), so, with the aluminium foil there will be more conduction then in the black or white polystyrene cups. There is a lot of convection, which affects the rate of energy loss because we will be using hot water, causing hot air to rise by conduction, and hot air rises and expands, so it will have to get out of the container. Knowing this helps me to make my prediction:
I predict that the painted black polystyrene cup will be the best radiator (losing the most heat the quickest), the polystyrene cup covered in aluminium foil will be the poorest radiator and the white polystyrene cup will be in between the other two, because of their surfaces. Also, because I will be using polystyrene cups in my experiment, this will make the container (cup) more insulated. We have also done an experiment using Leslie’s Cube (a cube which has 6 different variations of surfaces, for example: dull, dull and bright, dull and dark etc. ) whose evidence we have obtained from various tests, backs up my prediction.
Method: First, I will get out my equipment (see apparatus list) and set it up as shown in the diagram. I will then take the graduated measuring cylinder and measure a known volume (for fair testing e. g. in my experiment, 70ml), and pour the cold water into my first chosen cup (e. g. the plain white polystyrene cup) and mark the water level on the inside of the cup with the pen. After that, I will empty the cup and with the heatproof mat and lid, I will take the cup to the hot water tank and fill it up to the marked level indicated on the inside of the cup.
The starting temperature will probably be around 90 C. (In the case of possible repeats I may be using a slightly different starting temperature. ) Immediately after the cup is filled, I will put on the lid to prevent heat and energy loss, take it back to my working bench and insert the thermometer through the hole in the middle of the lid and take the first reading at 0 minutes and start the stop-clock. I will repeat this method for each cup. I will then be taking a reading every minute after that for a total of 10 minutes for each cup (i. e. 30 readings for all three cups in total).
If I decide it is necessary to do repeats for accuracy, averaging results (for an unbiased conclusion) and fair testing then I will be doing 60 readings in total. After I have finished the experiment, I will tidy my apparatus away safely, carefully and neatly. In this experiment there is no need to wear safety goggles, as I am not dealing with any corrosive substances. Fair testing: The following will be kept constant to make the test a fair one: 1. The equipment e. g. cups, thermometers and so on, so as to make sure that the conditions, amounts and properties such as temperature are kept the same.
2. The room temperature ( C) so excess heat from outside does not affect the rate of energy loss by radiation, conduction or convection. 3. The volume of water because we need to keep the heat energy levels the same and different amounts of water will affect factors such as energy loss. These are our constants. Our variable is the temperature loss (which cannot be manipulated). 4. The starting temperature i. e. for the first reading the starting temperature for all 3 cups will be 92 C and for the repeats (if necessary) it might be for example, 88 C (average being 90 C).
N. B – variables: Factors like timing (i. e. when we will take the readings and how long for) are our independent variables – this being the type of factor we will change step-by-step, deliberately. Our readings (results) are the dependant variables – the size or amount of this depends on the first reading. All of the other variables will be our constants – they will be kept under control. OBTAINING Preliminary experiments: For this experiment, my preliminary experiments went exactly according to my planning, method, as did my repeat.