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One experimental method of measuring an insulating material’s thermal
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- A hollow pure aluminum sphere with an electrical heater in the center is used in tests at steady-state conditions to determine the thermal conductivity of insulating materials. The inner diameter of the sphere is 0.350m; the outer diameter is 0.400m. For this test, the inner surface temperature of the pure aluminum sphere is held at a constant temperature of 250.0°C. The pure aluminum sphere is uniformly covered with an insulating material, 0.0900m thick. The outside surface of the insulating material is exposed to convection; T_inf = 22.0°C, h_inf = 25.0 W/(m2-K). The power required to keep the inner surface of the sphere at 250.0°C is 85.0W (this is assumed to be equal to the heat transfer rate, q). Ignoring contact resistance, determine the thermal conductivity of the insulating material, k.arrow_forwardSamples A and B are at different initial temperatures when they are placed in a thermally insulated container and allowed to come to thermal equilibrium. Figure (a) gives their temperatures T versus time t. Sample A has a mass of 4.96 kg; sample B has a mass of 1.35 kg. Figure (b) is a general plot for the material of sample B. It shows the temperature change AT that the material undergoes when energy is transferred to it as heat Q. The change AT is plotted versus the energy Q per unit mass of the material, and the scale of the vertical axis is set by AT, = 4.80 °C. What is the specific heat of sample A? 100 AT, 60 20 10 20 8. 16 t (min) Q/m (kJ/kg) (a) (b)arrow_forwardMonochromatic light (λ = 500 nm) is incident on a soap bubble (n = 1.40). What is the wavelength of the light (in nm) in the bubble film? Select one: O a. 255 O b. 700 O c. 357 O d. 422 O e. 500arrow_forward
- Samples A and B are at different initial temperatures when they are placed in a thermally insulated container and allowed to come to thermal equilibrium. Figure (a) gives their temperatures T versus time t. Sample A has a mass of 5.37 kg; sample B has a mass of 1.64 kg. Figure (b) is a general plot for the material of sample B. It shows the temperature change AT that the material undergoes when energy is transferred to it as heat Q. The change AT is plotted versus the energy Q per unit mass of the material, and the scale of the vertical axis is set by AT, = 4.10 °C. What is the specific heat of sample A? 100 AT A 60 20 10 20 8. 16 t (min) Q/m (kJ/kg) (a) (b) Number i Units T (°C) AT (C°)arrow_forwardWhile swimming, conduction can play a big role in heat loss from the body. The body of one swimmer has a total surface area of 1.80 m2 and an average thickness of 1.60 mm. The skin's thermal conductivity is 0.370 W/m-K. If the water's temperature is 20.0°C, and the blood reaching the inner surface of the skin is at 37.0°C, what is the rate of energy loss for that person through conduction?arrow_forwardSamples A and B are at different initial temperatures when they are placed in a thermally insulated container and allowed to come to thermal equilibrium. Figure (a) gives their temperatures T versus time t. Sample A has a mass of 4.79 kg; sample B has a mass of 1.50 kg. Figure (b) is a general plot for the material of sample B. It shows the temperature change AT that the material undergoes when energy is transferred to it as heat Q. The change AT is plotted versus the energy Q per unit mass of the material, and the scale of the vertical axis is set by AT, = 4.50 °C. What is the specific heat of sample A? Number i T (°C) 100 60 20 0 A Units 10 t (min) (a) 20 AT (Cº) AT, 0 8 Q/m (kJ/kg) (b) 16arrow_forward
- A copper bar is welded end to end to a bar of an unknown metal. The two bars have the same lengths and cross-sectional areas. The free end of the copper bar is maintained at a temperature TH that can be varied. The free end of the unknown metal is kept at 0.0∘C. To measure the thermal conductivity of the unknown metal, you measure the temperature T at the junction between the two bars for several values of TH. You plot your data as T versus TH both in kelvins, and find that your data are well fit by a straight line that has slope 0.460. What do your measurements give for the value of the thermal conductivity of the unknown metal? Use kCu = 385 W/(m⋅K) .arrow_forwardThe tungsten filament of a light bulb has an operating temperature of about 2100 K.If the emitting area of the filament is 1 cm2, and its emissivity (ε) is 0.68, what is the power output of the light bulb?arrow_forwardThe tube in a heat exchanger has a 2-in inner diameter and a 3-in outer diameter. The thermal conductivity of the tube material is 0.5 Btu/h·ft·°F, while the inner surface heat transfer coefficient is 50 Btu/h·ft2·°F and the outer surface heat transfer coefficient is 10 Btu/h·ft2·°F. Determine the overall heat transfer coefficients based on the outer and inner surfaces.arrow_forward
- The thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m · K and 0.020 W/m · K respectively, while other tissues inside the body have conductivities of about 0.50 W/m · K. Assume that between the core region of the body and the skin surface lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. Rskin m2 · K/W Rfat m2 · K/W Rtissue m2 · K/W R m2 · K/W (b) Find the rate of energy loss when the core temperature is 37°C and the exterior temperature is 0°C. Assume that both a protective layer of clothing and an insulating layer of unmoving air are absent, and a body area of 2.0 m2. Warrow_forwardThe thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m · K and 0.020 w/m · K respectively, while other tissues inside the body have conductivities of about 0.50 W/m · K. Assume that between the core region of the body and the skin surface lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. m² - K/W Rskin m² . K/W Rfat m² - K/W Rtissue |m² - K/W R (b) Find the rate of energy loss when the core temperature is 37°C and the exterior temperature is 0°C. Assume that both a protective layer of clothing and an insulating layer of unmoving air are absent, and a body area of 2.0 m2.arrow_forwardWhat is the rate of heat transfer by radiation, with an unclothed person standing in a dark room whose ambient temperature is 22.0ºC . The person has a normal skin temperature of 33.0ºC and a surface area of 1.50 m2 . The emissivity of skin is 0.97 in the infrared, where the radiation takes place.arrow_forward
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