On Heat Transfer

The last experiment of Physics 103.1 was all about heat transfer, particularly the three processes involved: conduction, convection and radiation. Basically, we did two experiments, the first of which was a test to see if the color of the container of a fluid would have an impact on the rate of cooling of the enclosed fluid. For this part, we compared black and white bottles. The patterns we obtained for both bottles were more or less the same: both were exponential functions with approximately the same slope. This agrees with theoretical knowledge since heat transfer in the set-up was through conduction via the walls. The color of the containers do not really factor in.

In the second part of the experiment, we looked at the effect of the color of a fluid's container on the rate of heating of the enclosed fluid. We used a lamp to induce heat transfer by radiation. In contrast to the graph of cooling, the graph of heating was a straight line.

This last experiment was quite short, similar to the other thermo experiments. Dealing with the bottles was quite nice since the tools remind me of Chem 16 days.

On the Gas Laws

The experiment this week focused on two simple equations that we encountered in our Chemistry classes: Boyle’s law and Charles’ law. The first states that, with temperature constant, the product of a gas’ pressure and volume at any point in time is a constant. The second states that, with pressure constant, volume divided by the temperature is a constant.

We were tasked to demonstrate the potency of these two laws using a syringe and heat engine apparatus. For Boyle’s law, we connected the syringe to the pressure sensor and manipulated the volume of the syringe by pressing down. We took the pressure reading and got P*V. Theoretically, P*V should be a constant but the measurements we obtained were not. We blame this error on the syringe-sensor interface. Since the interface was not secured, gas might have leaked out. For Charles’ law, we put the heat engine on its side and connected it to the air chamber can placed on a hot bath. We then cooled the temperature by constantly adding ice. We obtained V/t and saw that this also did not equal a constant. The error might have been due to leakage and improper V-t measurement.

On the Heat Engine

A heat engine is a device that converts thermal energy into other forms of energy. With that in mind, we were tasked to demonstrate the cycle of motion of a mass lifter heat engine composed of a piston attached to a system and an air chamber can.

A discussion of how heat engines work is not provided here. Suffice it to say, the engine cycle consists of two parts: the isobaric part (constant pressure) and the adiabatic part (no heat flow). These parts correspond to the addition/removal of mass on the piston, and the exposure of the air can to hot/cold temperature, respectively.

Initially, I was quite clueless with what to do with the piston apparatus, which costs P35,000 as repeated quite often by the person handling the equipment, since it was the first time for me to handle the device. It was not intuitive to me why the piston shifted height upon exposure of the air can to hot/cold temperature . I really had to think it over after the experiment. These deterrents caused me to be not much of a help with the procedural part of the experiment this week.

On the Freezing and Melting Point of Water

After a long hiatus, our Physics 103.1 lab resumed last Monday. What greeted us back was a relatively easy and quite fun experiment that dealt with the phase changes of water: freezing and melting. This entailed that we would be dealing with ice (which was fun to munch on) since we had to freeze tap water and monitor the temperature changes accompanying it. After creating ice, we boiled a cup of water and placed our newly frozen ice near the warm water. Similar to the first part, we measured the temperature along the way until the ice melted. 

Our results showed that the freezing and melting points were one and the same- that is, 0 deg celsius. Also, the plot of temperature vs time for the freezing part fitted an exponential graph with negative argument while that of the melting part had a constant part and an exponential part. We encountered a bit of a problem with freezing the ice because we forgot to put salt (which causes freezing point depression on the surrounding water used to freeze the ice). But otherwise, it was smooth sailing.