TEMPERATURE SCALES

TEMPERATURE SCALES

This first chart represent the relationship between Fahrenheit (F) and Celsius (C), even though three units are used in science, such as Fahrenheit, Celsius, and Kelvin (K). At the right upper side, students were able to determinate a mathematical equation that can describe or represent, if using a chart, the relation or how to pass from C and F, or vice-versa where the students would re-work the formula to pass from F to C.   

HEAT FLOW

On the second picture, students were asked to mix water. The first trial the temperature on the first coup was  65⁰ C (T₁) and on the second 25^o C (T₂), with both cups containing the same mass (100 g). By using the mathematical formula Avg=(T1+T2)/2. Since the masses are the same, by adding both and divide by 2 the average temperature was 45 ⁰ C. This process happens because the mass with more heat will seek to reestablish the equilibrium between both, with the hottest water given to the coolest one molecules that are full of energy, so the coolest molecules will absorb some of the energy and make the hottest molecules more stable.

On the second trial, the masses were differently and the water was not mixed. This time students had to place the hot water on one soda can and the cold water on a cup. The temperatures were the same, but the masses not. The soda cup had a total mass of 100 g and T₁ 25^o C, and the can the total mass was 50 g and T₂ 65^o C. The soda can was placed inside of the cup to see how fast both liquids could reach the equilibrium point. Since the can is made with aluminum, where its thermal conductivity is 250 Watts/meter-^oC, the mixer were able to reach the equilibrium, but not as faster as when both liquids were mixed. Using the same method and attending that the masses are different this time, the result is Avg=((m1*T1)+(m2*T2))/(T1+T2)= 38.3 ⁰ C. From this result, it can be read that by changing one parameter, the results also will be differently. 

THERMAL CONDUCTIVITY

The thermal conductivity represents how many Joules or how much energy is been transferred from one particle to another each second until both had reach the equilibrium. The picture shows how much heat was transferred to the copper bar. Using the formula Q=((kA(Th-Tc))/L, where Q is heat flow, k thermal conductivity of the substance, A Cross  -sectional area of the surface perpendicular to the heat flow, Th temperature of the hotter and/ the surface of the substance, Tc temperature of cooler and/ surface of the substance, L the distance in the medium in which the heat flows, and R=k/L the thermal insulation or resistance - bigger R, smaller heat flow.  Students were asked to calculate the heat flow for the copper (Cu) and aluminum (Al). Copper has a higher thermal insulation then the aluminum, since its k is 401 (watts/meter- ⁰ C) and the aluminum is 250  (watts/meter- ⁰ C). Those numbers shown that the aluminum has a better thermal conductivity and the energy flowing through it will pass faster than the copper bar. The Q for the copper is 123 J/s and Q for the aluminum bar is 123 J/s,  which means that the amount of energy that is passing each second through the bar of copper and aluminum. The interface temperature was found as to be the same 67.9 ⁰ C since both bars are connected which other.  

HEAT TRANSFER AS AN ENERGY EXCHANGE

In this last experience, students had to calculate how much heat is transferred. The first step was to see if the Immersion could delivery the amount of power that can be read in the label. This particular group found that the immersion had a power of 286.4 Watts (W). They measure the initial temperature of 100 ml of water and the readings were 22.6 ⁰ C. They also had to delivery some heat or transfer some energy during 20 seconds (s), and, as the first upper right graph shows, there was a transfer of energy with a linear relationship. That is, more heat transferring to the water, greater the temperature, and more energy is been delivering. 

The second graph, button left graph, represents the thermal conductivity versus the temperature. In this case, the relationship is also linear because higher the temperature, it will also represent an increasing on the quantity of heat that is been transferred to the water, which had a shallower slope. 

The third graph, middle down graph, is the relationship between temperature versus thermal conductivity. In this case, it can be read that the initial temperature is constant for a little while, but during the first 20 s, there is a slope that represents the amount of energy that was transferred from the immersion to the water.

If the mass is reduced to half of the initial amount, the amount of energy transferred to the water will be faster than the initial 100 ml as the button right graph shows, making the slope steep.