When objects heat up, most have a tendency to get larger. This is because the distance between atoms increases as they have more energy. To show this, we saw a bar that had each of its two sides made from different materials and predicted to which side would the bar bent to.
We predicted that the side that is made of invar would outgrow the side that is made out of brass and bent the bar as shown in the picture.
So Prof. Mason heated up the bar for us to see what happens.
And, he demonstrated the effect of thermal expansion on the bar. I took a video of it, but it is too big to be uploaded. Anyways, it turned out that the bar curved toward the side that is made out of invar, i.e. the brass side outgrew the invar side. He heated the bar from one side first and then cooled it to see the effect of heating the bar from the other side. The origin of the heat did not change the outcome. This shows that, even though both materials can be heated at the same time and to the same temperature, they expand at different rates.
Then Prof. Mason asked to which side would the bar curve to if it was cooled. My team's answer was:
This meant that the bar would bent towards the brass side. And, it did as Prof. Mason submitted the bar to ice for a few minutes.
After we had seen that materials expand and contract according to their temperature, we experimented to identify a metal based on how much does it expand when heated. For this, we set up a rotary motion sensor that could measure the change in length.
The tube was heated up using hot water vapor.
When the tube reached the temperature of the tube, the change indicated on the rotary sensor was recorded and used for calculation.
My group did the following calculation.
Then, we calculated the coefficient of thermal expansion to be 1.1 x 10^(-5) /C which turned out to be the one for steel. Hence, our tube is made of steel and we can use the coefficient to identify materials.
Next, we explored what happens when heat is added continuously to a mixture of ice and water.
And, we observed how the temperature rose as energy was added.
We noticed at first that the beginning looks bumpy for some reason. This was unexpected. But, it seems to be due to the mixture to the energy not being distributed evenly on all the water and ice.
Then, it started rising steadily.
Until it gradually stopped rising and turned into a flat line.
By following this reaction and the amount of energy added, we can calculate how much energy it takes to melt 1 gram of ice.
So, we designed our own experiment and wrote up our plan.
We started with 99.8 g of ice and 100 g of water.
Our set up looked somewhat like professor's.
And we got the following graphs.
The first one is a graph of Temperature vs. Time.
And the second one is a graph of Heat vs. Temperature.
It took about 2 min and 28 secs. for the ice to melt. With the energy delivered being at 297.8 W, the total energy spent in melting was 44,074.4 J. From the mas of ice, we obtain the heat of fusion to be 441 J/g. Then, from looking at the slope of the second graph we obtain the specific heat to be 4.381 J/gC. We let the water to boil for 25 secs until the heater was disconnected. And this was used to find the heat of vaporization, 2260 J/g. The percent discrepancies are 32.06 %, 4.83 % and 0% respectively.
These are the calculated uncertainties.
4.42 J/g of uncertainty belong to the heat of fusion. 659 J/g of uncertainty belong to the heat of vaporization. And, 0.07871 J/gC belong to the specific heat.
There are many possible sources of error in this experiment. Heat was also going towards the air and the cup. These quantities were not accounted for and were included as part of the behavior of water. So, this might the reason some of our values are higher than the accepted values. Also, the timing of the melting of ice and turning off the heater were probably off by a few seconds. Also, the power source was fluctuating during the experiment.
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