CC-logbook Lab week 8

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PHYSICS LOGBOOK TEMPLATE G Experiment logbook . Include your work from this week’s lab here. You will use this logbook later in the semester when you write your lab report. Lab Date: 12 / 2 /2023 Team : GROUP 9, Jack obrien, Max Meggitt GROUP 19: Mahmud Salih Asaroglu Tutor: Ben Field

Checkpoint 1: Logbook 1.1: Suppose that we keep apart two objects that have different temperatures so that no heat can flow between them. Are they at thermal equilibrium with each other? Although the objects do not interact with each other, they will interact with the environment. For example, a cup of water that is boiling and a cup of frozen water when left in a room for long enough will reach the same temperature and then they will reach thermal equilibrium. Logbook 1.2: Click Autoscale Graph and observe the two temperature graphs over time. Stop recording after about 7–10 minutes. Print the graph and attach it to your logbook. Logbook 1.3: Why did the temperature of the probe connected to the cold cylinder initially fall? The probe initially loses some heat to the cylinder as the probe is warmer than the cold cylinder it cools down causing the reading to fall as heat is transferred from the probe to the cylinder. Logbook 1.4: If we ignore this initial fall in temperature, would you expect the mean temperature of the two cylinders to be constant? What do you observe? Due to brass having high conductivity, it easily takes in energy from its environment, thus there are small but significant changes in its temperature. Thus it would not remain constant. However, if it is separated external loss of energy, it should remain constant. Logbook 1.5: Why might you expect the mean temperature to change with time? Are there other sources of heat loss or gain? Apart from (in this scenario) unpreventable heat loss such as radiation, there will be little amounts of airflow at room temp that will slightly increase the system’s heat, due to the tissue paper not being theoretically the perfect insulator for the system. Logbook 1.6: Why did we cover the Styrofoam cup with tissue? It is clearly not a very

good insulator The tissue acted as a barrier to prevent airflow and therefore convection from reaching the brass cylinder and potentially interfering with the testing environment as this experiment mainly focused on conducted heat transfer.

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Checkpoint 2: Logbook 2.1: What happens if T < Tenv? Use equation (1) to justify your answer. According to Newton’s Law of cooling equation, if T is less Tenv, the resultant term of T-Tenv would be a negative number. the product of the negative difference and the negative k constant would equate to a positive change, hence the object would begin to increase in temperature. Logbook 2.2: What do temperatures T1, T2 and T3 represent? How does the relative magnitudes of T1 and T3 to T2 explain the temperature profiles? T1 - A cool object which is being heated up e.g. a block of ice melting into water T2 - Temperature of the equilibrium e.g environment as it remains constant e.g. room temp 25 degrees T3 - A hot object which is being cooled down e.g. Hot water The relative magnitudes of T1 and T3 to T2 explain what the object are relative to each other (see examples) Logbook 2.3: List the decay constants κ1, κ2, κ3 from largest to smallest. Justify your answer. K1 = K3 < K2. K1 equals K3, it is just inverted (due to T1 having a negative outside of e, as T of 0 is lower than T of env). K2 has a steeper slope, indicating a lower exponent value, and as k has a negative outside it, a lower exponent means a higher k value. Thus K2 is the highest. Logbook 2.4: Time t = ln 2/κ is called the half-life. What does it represent? Half life represents the time taken for half of the thermal to be lost. It is exponential. Logbook 2.5: What is the value of temperature as t → ∞? What does this tell us? All T values reach a thermal equilibrium equal to the initial T2 value.

Logbook 2.6: Describe the graphs. Do they behave as you expect them? Do they (qualitatively) agree with the theory? The graphs do behave as expected as the brass which was in contact with brass saw the most transfer of energy and hence temperature increased the most at the fastest rate, while the wooden and free standing brass pieces which had a much slower increase in temperature due to poor conductors of heat being used (air and wood). This is demonstrated by the slope o the graph, which if continued would plateu as the brass objects reach thermal equilibrium with the room temp. Logbook 2.7: Print your graphs after zooming them and placing the data boxes appropriately. Attach the graphs to your logbook.

Logbook 2.9: Identify and write down the decay constants κb, κw and κa for the heat transfer between cylinder and brass block, wood and air, respectively. Are they as expected? Justify your answer. Kb C = 0.0086 +-0.0005 Kw C = 0.0019 +-0.0002 Kc C = 0.0010 +- 0.0001 Kb is the largest as the metal slab is the most thermal conductive material, Kw is the second largest as although wood isnt a very good conductor of heat it still transferred energy and it was a better thermal conductor than air as air is not good a dissapating heat and hence air is smallest in value. kb > kw > kc Checkpoint 3: Logbook 3.1: It is possible that the rods have not reached thermal equilibrium (i.e. constant temperature over time) by the time you make measurements. However, they will have reached steady state: in this context, the relative values of the temperature readings at the four locations along the length of the rods remain unchanged. How does the fact that the rods are not at thermal equilibrium affect the value of thermal conductivity k? When a group of objects are not at thermal equilibrium, the temperature and heat energy are not distributed evenly throughout the system. This means that the thermal conductivity k may be affected, as it is a measure of how easily heat can be transferred through a material. Overall, the fact that the group of objects are not at thermal equilibrium can affect the value of thermal conductivity k, as temperature gradients and differences in thermal conductivities can lead to variations in how easily heat can be transferred through the system. Draw a sketch of the apparatus, making sure to identify and label the power sources, connecting leads, metal rods and temperature sensors.`

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Logbook 3.2: Record the probe temperatures of the rod at four different times (separated by at least 20 s). Is the rod at thermal equilibrium? If not, is it in steady state? How do you tell? Proceed only if equilibrium or steady-state has been reached, otherwise, wait. They are not in thermal equilibrium, they are in a steady state, this is reflected by the rods having different temperatures but the temperature not fluctuating. Logbook 3.3: Record the temperature along the length of all rods at four different times. Hole Time (sec) Temp of Copper 19mm purple Temp of Brass 12mm green temp of copper 12.7mm yellow Uninsulated temp blue 1 20 30.1 37.8 31.6 30.25 2 40 29.6 35.3 30.8 29.4 3 60 29.2 32.8 30 28.7 4 (closest to heat sink) 80 28.7 30.5 29.2 28.1 Logbook 3.4: For each measurement calculate the heat conductivity k and then the average heat conductivity for each rod with its uncertainty. You may want to use Excel to do these calculations.

Logbook 3.5: How do your values compare with the accepted values of heat conductivity for copper and brass? Accepted value: Copper – 398 W/m•K Calculated value: Copper - 369.49 W/m•K Accepted value: Brass - 111 W/m-K Calculated value: Brass - 149.63 W/m-K When comparing the values they are close to the accepted values. Logbook 3.6: How does convection affect heat conductivity? Convection can affect heat conductivity by either enhancing or reducing the overall heat transfer rate.. In the case of convection, if the fluid or gas is in motion, it can increase the overall heat transfer rate by carrying heat away from the source and distributing it more evenly throughout the medium. This is because the movement of the fluids or gases can create a boundary layer of stagnant fluid at the surface of the solid, which can reduce the heat transfer rate through conduction.

Completion: 1. A fan in fact generates heat when running. How does it actually help us cool down during summer? By blowing air around, the fan makes it easier for our body to evaporate sweat from our skin, thus making us feel cooler. Ceiling fans also allow cold air to rise to our heads as it pushes the hot air down. 2. Why does a metal object at room temperature feel colder to the touch than a wooden block of the same temperature? The metal object is a much better thermal conductor, so when heat transfers from the environment and our skin into the metal object, the heat transfers to the bulk of the object, leaving our skin and the surface cool. The wooden object is not, thus there is a higher ratio of heat left on our skin and the surface. 3. What role does the heat sink play in this experiment? The heat sink is a device that is designed to dissipate or transfer heat away from a hot surface or component, such as an electronic device, engine, or power supply. The primary role of a heat sink is to maintain the temperature of the hot surface at a constant temperature.

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