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, what we did this week was 2 experiments- the first of which was a test if whether the color of the container of a fluid had an impact on the rate of cooling of the fluid it encloses. 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 through the walls- the color of the containers do not really factor in.

The second part of the experiment was basically comparing the effect of color of the container of a fluid on the rate of heating of the enclosed fluid. We used a lamp for this part to induce heat transfer by radiation. As contrasted 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 and the graduated cylinder was quite nice since these tools remind me of Chem 16 days.

On the Gas Laws

The experiment this week focused on a two simple equations that we encountered in our Chemistry classes- Boyle’s law and Charles’ law. The first states that for an ideal gas with its temperature constant, the product of the gas’ pressure and volume at any point in time is a constant. On the other hand, the second states that for an ideal gas with pressure constant, the 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 pushing down. We took the pressure reading and got PV. Theoretically, PV should be a constant but what we obtained was 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 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 (with trapped air) which is also connected to an air chamber can.

A discussion of how a heat engine works is not provided here. Suffice it to say, the engine cycle consists of two parts: isobaric part (constant pressure) and 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. Also, the reason why the piston shifted height upon exposure of the air can to hot/cold temperature was not intuitive at first. 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.