Evaporation
This form of heat transfer is a result of the particles of a liquid (normally water) being given thermal energy and breaking away from their group. This makes the water ‘evaporate’ into steam. This steam can be very hot and contains a lot of pressure. An example of a piece of equipment that uses evaporation is a kettle.
Other scientific knowledge that will help me in my investigation are:
Specific Heat Capacity
Specific heat capacity is the “quantity of heat required to raise the temperature of a unit of mass of a substance by a unit change in temperature.” To calculate the energy that has to have been transferred to an object in order to course a temperature rise the following equation can be used: Q = mcT and the word equation is: energy transferred = mass x specific heat capacity x temperature change. Where Q is the change in heat content in Joules, m is the mass in kg, c is the specific heat capacity in J/ (kg °C), and T represents the temperature change in °C or K. The specific heat capacity of a substance is dependent upon its phase and molecular structure. Heat capacity is the mass of an object multiplied by the specific heat capacity resulting in the quantity. The heat capacity is the amount of heat required to increase the temperature of an object by
Factors that effect temperature rise
A factor that affects the temperature rise is the mass of an object. This is because there are more particles to heat up than in an object of smaller mass. For example, a jug of 50cm ³ will heat up to 30°C a lot quicker than a tub that has 500cm ³ of water inside, although the tub will contain more energy than the jug of water. This is because there are more particles to heat up in the tub of water than in the jug of water.
To make sure that my practical is a fair test, I must take the following factors into consideration:
Room Temperature – The room’s temperature must be the same for the entire practical. This can be made possible by carrying out all experiments in the same room.
Time – I must take the same amount of time for each experiment. I must not allow any extra time in the experiment. This aim will be met by simply using an accurate stopwatch.
Material Temperature – The temperature of all the materials should be the same throughout the investigation. This is because if some materials are hotter in one experiment than another, then it will not be fair as this may alter the temperature of the object. To control this I will let each material cool down before the next experiment.
I must use the same apparatus – This is to make sure that no experiment has an advantage over another. To do this I will just set up the equipment with the same apparatus.
I must use the same voltage – I must use the same amount of voltage to power the electric heater. This is because, if I use a higher voltage to heat up the heater, it will get heated faster than the other times. To control this, I will use a volt-box and I will keep it at the same voltage throughout the experiment.
The apparatus that I propose to use are: A power supply, Ammeter, Voltmeter, Immersion Heater, Thermometer and a one kilogram block. Once the apparatus is all set up, it will look like the following:
I propose to use a 1kg block, for ease of calculations. I will measure the temperature of the block with a thermometer, which will be inserted directly into the 1kg block. I will measure the temperature ten times with sixty second intervals. From this I will be able to calculate the amount of energy required to raise the temperature by 1. To calculate the amount of energy that is used I will use the following formula: I x T x V = electrical energy. To improve my accuracy when carrying out the experiments, I will use a clear thermometer, so that I can easily read it. Also, to improve total accuracy, I will use as much digital equipment as possible. E.g. A digital voltmeter, ammeter and stopwatch. The reason for using these digital pieces of equipment is that they can accurately tell you the numbers, which eliminate the errors made when reading analogue equipment with the naked eye. A safety precaution that I will need to take is to keep all other objects that emit heat (e.g. my hand, etc) away from the actual experiment. This is because these objects may interfere with the final results.
The variables are factors that I will change throughout the experiment. These variables are: The temperature rise and the mass of the object. The constant is something that is always the same throughout the whole experiment. The constant in my experiment is apparatus and the time that each material is heated for.
To prepare for the actual experiment, I carried out some preliminary work. This preliminary work was simply carrying out a ‘fake’ version of my experiment to see what changes need to be made to make it more accurate. As I carried out this preliminary experiment, I recorded the results down.
The starting temperature was 26.5°C.
During this preliminary experiment, I used 12 volts. After carrying out the experiment, I realised that my procedure was incorrect as there was significant heat loss. The error that I made was that the 1kg block had a rather big hole, which had a much wider circumference than the immersion heater. This meant that there was a lot of heat loss as there was such a big gap between the two objects. For my final experiment I will make sure that the immersion heater fits exactly into the object to reduce any heat loss.
I predict that the experiment will show that for the given mass, the higher the energy the higher its temperature. I can also predict that the results graph will look like this:
I know that this is how the graph is going to look because there is a positive correlation between O°C an E. Meaning that there is a direct linear relationship between O°C an . I can also predict what the energy will be by using the equation E=MCO as shown below:
From e above predictions you can see how much energy it takes to increase the temperature by 0°C, 1°C, 2°C, etc. Now I must carry out the actual experiment to see if my predictions are correct.
I have obtained some of my information from my school exercise book and my school text book ‘Complete Physics’. I have also used a science encyclopaedia.
After carrying out my preliminary experiment, I am ready to do the final experiment. So I set up the experiment with the relevant adjustments. I also added some insulation to the 1kg block to reduce heat loss through conduction. The results of the final experiment are shown below: (starting temperature = 26°C)
Mean Average Temperature = 33.4°C
The method used to perform this experiment is as follows:
- Set up the experiment as shown in diagram
- Add insulation (only to final experiment)
- Start the stopwatch simultaneously to the power being switched on
- Record the Amps and the Volts
- Record down the temperature every sixty seconds.
The changes that I made to the final experiment seemed to have made some difference as the ending temperature of the preliminary experiment was 36°C whereas; the ending temperature in the final experiment was 40°C. I think that using a 1kg block that fitted exactly with the immersion heater made the most difference to the results as it prevented a lot of heat loss.
A precaution that I took to make sure that my readings were more accurate was to make sure that I started the stopwatch at exactly the same time as I switched the power on.
After collecting all my results, I created a line graph with the data:
My initial prediction for the mathematical relation ship was: ‘the experiment will show that for the given mass, the higher the energy the higher its temperature’. This prediction has been proven correct by the final results.
If you look at the graph above, you can see the positive correlation which illustrates the trend: The higher the energy the higher the temperature, which means that it corresponds with my initial prediction.
I think that my method of carrying out this experiment was a good method, as it did provide me with fairly accurate results. My final method was good because of the changes I made to it with the information I collected in my preliminary work. I think that my method was fairly accurate because I started the stopwatch timer at exactly the same time as I switched the power on. This ensured that there was no extra power given to the immersion heater before the actual experiment was recorded.
If I did my experiment again, I would the main improvement that I would make is to use brand new equipment. This is because I used the equipment provided by the school, which was quite old and fairly used. This meant that there was a good chance that the results were recorded with faults. This may have been the case because some equipment may not have been doing there job accurately. For example, the schools immersion heater was quite old and had been used a lot before, this meant that the immersion heater may not have been emitting the correct amount of heat energy.
Looking at all the inaccurate equipment, leading to the potentially incorrect results, I think that my results are not accurate enough to draw firm conclusions. This is because one faulty piece of equipment can lead to an array of inaccurate results which could lead to erroneous conclusion, and the schools equipment being faulty is far too possible to be a reliable source of results.
Another experiment that could be carried out to extend the work that I have done is an electrical conductivity experiment. This experiment could analyse the relationship between the rate of electrical conductivity and the mass of an object; although, this experiment would need very accurate pieces of equipment.
By Usman Naeem