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.

On Resonance and Sound

In contrast to our experiment last meeting (Calorimetry), we performed an experiment regarding waves this week. Specifically, we performed an experiment which demonstrated resonance, the increase in amplitude of vibration of a body due to the constructive interference of the driving force of the vibration’s frequency and the body’s characteristic frequency of vibration.

Using a resonance “tube” filled with water and a speaker of constant frequency on top of the tube, we looked for the water levels wherein the sound volume was at a maximum. These water levels correspond to the length of the tube that allowed standing waves to be set-up. Also, at these water levels, resonance was observed. By getting the average of the difference between the distance where resonance was observed, we were able to obtain the wavelength using ΔL=½λ. Finally, using v=fλ, we obtained the speed of sound in the tube.

The experiment was quite difficult because it required us to hold the speaker manually above the tube. It was tiring so we took turns doing it. Also, water from the tube unfortunately spilled on the floor which caused quite a mess. Apart from these, I thoroughly enjoyed the experiment because we had good group dynamics.

On Heat and Calorimetry

Entering the 103.1 lab, I saw a gas stove set up. Asking what it for, I found out that we would be performing an experiment on Thermodynamics.

I consider Thermodynamics to be my favourite subject in our General Chemistry courses (16 and 17). Unfortunately, I have forgotten quite a deal on the said subject, so it was nice to rekindle my interest in thermodynamics by performing a simple calorimetry experiment this meeting.

Basically, what we did was mix hot and cold water together and measure the enthalpy change (ΔH=mcΔT) to see that the heat lost by the hot water and the heat gained by the cold water were equal. It was quite an easy experiment, though numerous little niggles cost us time. For one, the balance used to measure the mass of the calorimeter was in the other room so we had to go back and forth between rooms (though this was remedied eventually), and a short brownout occurred which we had to wait out to be able to use the balance.

Overall, the experiment was quite a simple task to perform. Compared to the experiments in 102.1, this experiment was a walk in the park.

On Light Intensity

The second experiment we performed was all about light intensity. To cut the story short, it was a quick experiment, not taking up more than 30 minutes. It was a relatively easy task--- we simply measured the light intensity from a light source and a laser at different distances from the light source using a light sensor connected to labquest.

From the graph of light intensity vs. distance from light source, we observed an inverse square law; that is, the light intensity is inversely proportional to the square of the distance from the light source. This conclusion was obtained using data from the light source (not laser). The data we got from the laser showed that light intensity was constant even at great distances. It could probably be the case that the intensity from the laser was so high that very great distances would be called for to see the inverse square law.

We encountered minimal error, if none. I think our group had good dynamics because we finished the experiment in record time. I hope that the next experiments are going to be as easy as this, so that we would always finish ahead of time. :D