Physic 2.

To measure the Thermal Conductivity of a material Lab 5 video link: http://youtu.be/t1Np-Xk1pSM 1. Objective: To measure the coefficient of thermal conductivity of the following substances. Masonite, wood, lexan, sheet rock and glass. 2. Equipment: Thermal conductivity apparatus consisting of a base, steam chamber with mounting brackets, ice mold with cover, masonite, wood, lexan, rock and glass 3. Theory: The rate at which heat is conducted across a substance is given by Q k A  = t x where Q is the total amount of heat conducted in a time t k is the coefficient of thermal conductivity A is the area of the conducting surface and x is its thickness  is the difference in temperature between the two faces. k= Q x W / mK A  t The actual thermal conductivities of the materials are given below: Therefore, Substance Masonite Wood Lexan Sheet rock Glass K (W/(m.K)) 0.047 0.11-0.14 0.19 0.43 0.72-0.86 4. Procedure: 1. Measure and record the thickness of the material, x 2. Run the jar under water to loosen the ice so that ice can move freely in the jar. Do not remove the ice from the jar. Measure the diameter of the ice block and record it as d1. 3. Place the ice jar on top of the sample so that the open end is in contact with the sample. Let the ice sit for several minutes on top of the sample so that it melts and comes in contact with the sample. Do not take any data at this time. 4. Obtain the data for determining the ambient melting rate of the ice as follows (i) Determine the mass of the small beaker (ii) Collect the melting ice in the beaker for 10 minutes (iii) Measure the total mass (beaker + water) (iv) Obtain the mass of melted ice and record it as m 5. Run steam into the steam chamber. Run the steam for several minutes so that the heat flow is steady. Collect melted ice for 10 minutes, measure its mass and record it as M. 6. 7. Measure the diameter of the ice block and record it as d2. 𝑑 +𝑑 Calculate the average diameter d of the ice as 𝑑 = 1 2 2 Repeat steps 1 through 7 for four other materials. 5. Calculations: 1. Determine d, the average of d1 and d2 and find r = d/2. Calculate the area of the ice block in contact with the material as A =  r2. 2. Determine M – m which is the mass of ice melted due to heat transmitted through the material. Then Q = (M – m)  3.34 x 105 J 3. Calculate k using the equation k =  = 100 and t = 10 min = 600 s 4. Q x A  t W / m  K where Use the actual value of k to determine the percentage error. Important note: In addition to putting your measured and calculated values in the data table, you need to record for each material the quantities  x, detailed steps for calculating d, A, m, M,  Q, and detailed calculation steps to show how k is calculated. Use the name of the material as sub-titles. There is no graph for this lab. DATA: mater x d1 d2 d r A (m) (m) (m) (m) (m) (m2) ial Maso nite Wood m (kg) M (kg) (M-m) (kg) calc. k W/mK actual k W/mK 0.047 0.12 Lexan 0.19 Rock 0.43 Glass 0.80 6. Questions: 1. What is thermal resistance R of a substance? x If R = , calculate the thermal resistance of the five materials using your kA calculated k values. What is the thermal resistance of a series combination of rock and glass? What is the resistance of a parallel combination of rock and glass? Calculate the thermal current through each of the five materials Which of the five materials is a better insulator? Why? 2. 3. 4. 5. 6. % error

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