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Conduction is best in solids and considerably weaker in liquids and gases. This transfer relies on the movement of atoms and molecules.
For example, if a part of a material is hotter than another part, then the hotter part has more energy than the surrounding parts. Whenever you heat any substance there is an increased amount of motion from atoms and molecules. When you heat a gas, for example, the speed at which the atoms and molecules move around increases but when you heat a solid or even a liquid the atoms and molecules vibrate more. The atoms and molecules in the substance are therefore responsible for conduction. In a gas and liquid, conduction is poor because the atoms and molecules are further apart than in a solid where they are closely held with strong bonds.
Metals such as silver, copper and aluminium are good conductors.Convection takes place only in fluids (liquids and gases). Convection currents are examples of floating and sinking. When a part of a fluid is heated and made warmer the molecules expand and rise because they are less dense than the cold parts of the fluid where the molecules sink downwards because they are more dense.All objects give out some thermal radiation. The higher the temperature of any object the more energy it radiates per second.
The thermal radiation is most of the time given out as infrared waves (invisible) but very hot objects give out light waves (visible). A matt black surface is the best emitter and absorber of heat energy but is the worst reflector. A white or silver surface is a poor emitter and absorber but a very good reflector.Evaporation is the process where particles from a liquid form a vapour when the temperature of the liquid is below its boiling point. Evaporation can only take place from the surface of a liquid. This is because here the molecules have enough energy to evaporate, as there are less attractive forces from neighbouring molecules preventing it.Factors that May Affect the Heating Effect2 The voltage of the power supply could be measured using a voltmeter and a varying nominal voltage on the power supply. Though an increase in voltage would result in an increase of the current in the circuit, therefore it is not an independent variable.3 The starting temperature of the water and room must be kept constant for a fair experiment. To keep the water at the start the same temperature we should replace the water every time we finish a list of readings. Some parts of the room may be at different temperature than others and so it is difficult to keep the room temperature constant.4 The material of the beaker or cup will be an important factor as different materials are good at conducting and radiating heat energy. For example, a polystyrene cup would reduce heat loss as it acts as insulator.5 The mass therefore the volume of the water is important because different amounts of water will take different lengths of time to be heated and so we must keep the mass or volume of the water the same throughout every experiment.6 The depth that the heating element is submerged in the water should be the same every time and have the same position e.g. the center for each experiment.7 External air pressure would vary but in this experiment an airtight room is not available to use.8 The internal resistance of the heating element as the greater the resistance the slower the rise in temperature of the water but resistance will be affected by both the current and the voltage.For my experiment, I have chosen to vary the current while keeping the all the other factors constant. It is important that the other factors are kept constant for a fair test and to show that a change in current will actually affect the rise in temperature of the water.MethodApparatusA few electrical wiresSome aluminium foil1ï¿½ Beaker1ï¿½ Heating Element1ï¿½ Thermometer2ï¿½ Clamps1ï¿½ Glass rod1ï¿½ Voltmeter1ï¿½Ammeter1ï¿½ Variable Resistor1ï¿½ Battery Pack1ï¿½ Stopwatch1ï¿½ Retort Stand1ï¿½ BalanceDiagramIn this experiment we are measuring the rise in temperature over a fixed amount of time, which here is 5 minutes. The heating element should be connected in series to a DC battery pack using 12V, an ammeter and a variable resistor in series with a voltmeter parallel to the heating element. The heating element would then be submerged into the beaker, at the same depth every time, that is covered inside and outside with aluminium foil. Aluminium is a good conductor and therefore is a better one than glass, which is a poor conductor. Aluminium foiled is used to reduce the heat loss because when the beaker is covered there remains a small gap of air between it and the aluminium foil. We know from theory that air is a very poor conductor therefore we are reducing the heat loss, which is what we want. The beaker should contain 200cm3 of water with a mass of 202g. Both the glass rod and thermometer should then be placed into the beaker. The glass rod is used to stir the water so that it is uniformly heated and the thermometer is needed to record the temperature of the water.For the first experiment, the current should be 0.5A having set this current using the variable resistor we should place the heating element into the water and start the stopwatch. Then record the temperature every 30 seconds using the stopwatch. When it has been 5 minutes the battery back should be switched off and the heating element removed from the water. Now we have completed the first experiment using 0.5A. Before changing the current to 1A we should first let the heating element cool down for a few minutes so it can be acclimatised to the temperature it was used for 1A. Secondly the water should be replaced with the same type of water used, e.g. tap water and then the mass should be the same also. We need to replace the water because if we don’t then the heat losses are not going to be the same every time. The beaker would therefore be emptied and then should be washed out and allowed to cool before the next experiment. The current then should be set to 1A and the temperature recorded for the next 5 minutes. These steps should be repeated up to 5A and 5 minutes for each of the current readings.Safety PrecautionsIt is necessary to wear safety goggles to protect the eyes even though the temperature of the water will not be high enough for it to boil. The apparatus should not be placed at the end of the bench and all water should be handled carefully without spilling any on the electrical equipment and wires being used. When moving or dealing with the hot heating element after each experiment, it should consider that you hold it from the rubber end where it is not hot.PredictionI predict that as the current increases the heating effect of the heating element will increase therefore the water will rise to a higher temperature in a shorter space of time. I predict this because if there is a higher current passing through the heating element then it will heat up the water even more. If this happens then there is a larger transfer of electrical energy to heat energy taking place. This can be proven by this equation:That can be made simpler into:If we can find out how much energy the heating element gives out into the water then we are also able to find out how much heat energy is absorbed by the water using this formulae:The specific heat capacity of water is 4200 J/kg/?C (Complete Physics; Stephen Pople).Bibliography1 My own knowledge2 Physics Classbook; Graham Booth3 Complete Physics; Stephen PopleTo Investigate the Heating Effect of an Electric CurrentCollection of DataTemperature ?CTime (s)03060901201501802102402703000.519191919202020202020211.019191919202020212121221.519191920202121212122232.019202020212122232323242.519202020212121222323253.019202021222223242525263.519202121222324242526264.019202122232424252627284.519212122232425262728295.01921222324252628293032To Investigate the Heating Effect of an Electric Current1 As I predicted the change in temperature increased as the current increased therefore the water was getting hotter quicker as the current got higher.In order to show a pattern or trend from my results, I need to be able to plot a graph therefore I have made this table using my “Collection of Data” in the Obtaining Evidence section.I/AI2/A2?Q/ï¿½C0.50.2521.01.0031.52.2542.04.0052.56.2563.09.0073.512.2574.016.0094.520.25105.025.00