Transmission of heat Questions and Answers

How much heat is required to vaporize 5 7 kg of water at 100 C

3 A chemist mixes 500 g of lead at 500 C with 1 200 g of water at 20 C She then mixes 500 g of copper at 500 C with 1 200 g of water at 20 C The specific heat capacity of lead is 0 1276 J g C and the specific heat capacity of copper is 0 3845 J g C What will be true about the final temperatures of the two systems O A The final temperature of the lead water system will be equal to the final temperature of the copper water system O B The final temperature of the lead water system will be higher than the final temperature of the copper water system OC The final temperature of the lead water system will be lower than the final temperature of the copper water system O D Cannot be determined from the given information

A steel bar 9 cm long is welded end to end to a copper bar 21 cm long Both bars are insulated perfectly on their sides Each bar has a square cross section 2 0 cm on a side The free end of the steel bar is maintained at 100 deg C by placing it in contact with steam and the free end of the copper bar is maintained at 0 deg C by placing it in contact with ice Find the temperature in deg C at the junction of the two bars kst 50 2 W m K Kcu 385 W m K Round your answer to 2 decimal places

A rod 43 cm long is made of steel and has a cross sectional area of 2 21 cm The temperature at one end of the rod is 0 deg C while the other end is 100 deg C What is the heat flow W in the rod in the final steady state kst 50 2 W m K Com Round your answer to 2 decimal places

One end of an insulated metal rod is maintained at 100 deg C and the other end is maintained at 0 deg C by an ice water mixture The rod is 61 cm long and has a cross sectional area of 1 25 cm What is the thermal conductivity W m K of the rod if heat current is 4 91 W Round your answer to 2 decimal places

At what net rate does heat radiate from a 300 m black roof on a night when the roof s temperature is 13 35 C and the surrounding temperature is 39 02 C The emissivity of the roof is 0 888 Round your answer to 0 decimal places

Radiation makes it impossible to stand close to a hot lava flow Calculate the rate of heat transfer by radiation from 1 25 m of 1342 C fresh lava into 38 C surroundings assuming lava s emissivity is 1 00 Round your answer to 0 decimal places

At what net rate does heat radiate from a 284 m black roof on a night when the roof s temperature is 15 8 C and the surrounding temperature is 38 33 C The emissivity of the roof is 0 855 Round your answer to 0 decimal places

Cherry red embers in a fireplace are at 960 C and have an exposed area of 0 39 m and emissivity of 0 895 The surrounding room has a temperature of 17 49 C If 77 of the radiant energy enters the room what is the net rate of radiant heat transfer in kilowatts Round your answer to 0 decimal places

MY NOTES ASK YO A sample of iron with a mass of 1 95 kg initially at a temperature of 150 0 C is in a well insulated container Water at a temperature of 20 0 C is added to the container and the entire interior of the container is allowed to thermal equilibrium where it reaches a final temperature of 67 0 C What mass of water in kg was added Assume any water turned to steam subsequently recondenses 0 36 X kg

Bob makes coffee for his boss Jill every morning Jill wants her coffee exactly 102 degrees The coffee coming out of the pot is 140 degrees and the office is 71 degrees Bob knows that after 5 minutes the coffee is 120 degrees How long should Bob wait after making the coffee to deliver it to Jill Use Newton s heating cooling law that the rate of change in the temperature H is proportional to the difference between the object and the surrounding temperature O 10 382 O 11 241 O 11 680 O 12 536

28 A Use arrows to show the direction of heat transfer B Draw 2 arrows for fast heat transfer br C Which object has no internal energy 0 C conductor 35 C conductor 10 C insulator

as at 100 C fills volume Vo Y Part A If the pressure is held constant by what factor does the volume change if the Celsius temperature is doubled VAE Submit Part B Request Answer If the pressure is held constant by what factor does the volume change if the Kelvin temperature is doubled Review

24 Conduction N Convection V or Radiation R Cooks pasta in a pot of hot water Heats the water throughout the pot A B C Heats your hand next to but not touching the pot 25 A heat lamp is placed near two objects which one changes temperature faster A black one or a white one The dull one or shiny one One made up of gold or aluminum A B C

NTERACTIVE EXAMPLE Calculations Involving Specific Heat Capacity What quantity of energy in joules is required to heat a sample of aluminum weighing 2 11 g from 23 0 C to 50 0 C The specific heat capacity of 0 89 J g C HOW DO WE GET THERE However we want to raise the temperature of our sample by more than 1 C What is the temperature change that occurs Temperature change C

INTERACTIVE EXAMPLE Specific Heat Capacity Calculations Using the Equation A 2 5 g sample of a metal requires 10 8 J of energy to change its temperature from 23 C to 41 C Using the given information and table below determ identity of the metal Substance Specific Heat Capacity J g C aluminum s 0 89 0 50 0 45 0 38 0 24 0 13 nickel s iron s copper s silver s gold s HOW DO WE GET THERE We can represent the data given in this problem by the following diagram 2 5 g metal T 23 C 2 5 g metal 10 8 J T 41 C What is the temperature change AT that occurs Temperature change AT

Two objects with different sizes masses and temperatures are placed in thermal contact Choose the best answer O Energy travels from the object at higher temperature to the object at lower temperature O Energy travels from the larger object to the smaller object O Energy travels from the object with more mass to the one with less mass

pressure atm Question 13 of 23 4 0 3 0 Question 14 of 23 2 0 1 0 0 0 Mark for Review What s This 100 1 Points ck to see additional instructions estions 11 15 Shown here is the PT phase diagram for an unknown substance First identify the ostance s state of matter in each of the three large regions of the diagram Then answer the following estions At 2 0 atm pressure the substance s boiling point is approximately 200 300 temperature K 1 Points 400 K

What is the geothermal gradient in a volcanic arc where the temperature is 202 C at a depth of 5 6 km Assume a surface rock temperature of 10 C geothermal gradient C Jan

The lifetime of a star can be estimated in solar lifetimes by dividing 1 by the mass of the star raised to the 2 5 power T 1 M2 5 where mass is given in solar masses What is the expected lifetime of a star that has one third the mass of the Sun T solar lifetimes

After sitting out of a refrigerator for a while a turkey at room temperature 68 F is placed into an oven The oven temperature is 315 F Newton s Law of Heating explains that the temperature of the turkey will increase proportionally to the difference between the temperature of the turkey and the temperature of the oven as given by the formula below Ta the temperature surrounding the object To the initial temperature of the object t the time in hours T Ta To Ta e h kt T the temperature of the object after t hours k decay constant The turkey reaches the temperature of 114 F after 2 5 hours Using this information find the value of k to the nearest thousandth Use the resulting equation to determine the Fahrenheit temperature of the turkey to the nearest degree after 5 hours Enter only the final temperature into the input box

26 An adiabatic process is performed on 15 moles of an ideal gas y 1 44 What is the heat capacity at constant pressure for the gas Let the ideal gas constant R 8 314 J mol K 29 J mol K 27 J mol K 31 J mol K 23 J mol K 25 J mol K

All changes saved 11 A radiating body has a Kelvin temperature To and its surroundings are at 500K To 500K When the Kelvin temperature of the radiating body increases to 2To the net rate of its radiation increases by a factor of 39 What is To 523 K 512 K 540 K 567 K

When an electric mixer is used to vigorously stir a bowl of room temperature water the mixer is doing mechanical work on the water Assuming no heat is added or removed from the water what will happen to the water s temperature O The temperature of the water will remain unchanged O The temperature of the water will decrease O The temperature of the water will increase

0 A thin square steel plate measures 14 cm on each side and has emissivity of 0 60 The plate is heated to a temperature of 745 C What is the rate at which the plate radiates energy The Stefan Boltzmann constant is 5 67 10 8 W m K4 Remember that the plate will radiate energy from both its top and bottom surfaces O O 720 W 3 4 kW 590 W 1 4 kW

2 Which material if any is the best thermal insulator material C In an experiment a thin sheet of material A B or C was used to divide two objects of different temperature In each trial the conditions were identical except for the material of the thin sheet The data table shows the times in which the objects reached thermal equilibrium material A material B Material All three are equal insulators A B C Time to reach equilibrium 5 minutes 30 minutes 110 minutes

equilibrium 5 minutes 30 minutes 110 minutes In an experiment a thin sheet of material A B or C was used to divide two objects of different temperature In each trial the conditions were identical except for the material of the thin sheet The data table shows the times in which the objects reached thermal equilibrium Which material if any is the best thermal conductor All three conduct heat equally well material C material B material A Material A B C

14 Rod X and rod Y are cylindrical rods made of the same metal Rod X has radius r and length L Rod Y conducts heat at the same rate as Rod X Which could be the dimensions of Rod Y O O radius 2r length 44 radius 2r length 21 radius r length 21 radius 4r length L

Water Ice Students design an experiment with a curved insulated rod of an unknown thermally conducting material as shown in the figure The rod is 1 m long and 2 cm in diameter One end of the rod is touching the surface of vater kept at 350 K by a hot plate and the other end is just touching the surface of a well insulated block of ice The students are required to create a procedure to determine the thermal conductivity of the rod They first determine that they can measure the amount of ice that has melted after a given time to calculate the heat ansfer over time to the block of ice Which of the following must the students also measure to calculate the thermal conductivity of the rod

Convection of Liquids Tube Demonstration Observations Draw the path the dye takes through the convection tube Discussion Questions 1 Describe what is occurring in the convection of liquids tube during the demonstration 2 Name at least two other examples of convection in everyday life situations Ice melting a hot cup of tea 3 Did the movement of the water change over time If so how yes it started moving faster 4 Other than convection what other method of heat transfer was taking place in the demonstration

A 0 478 kg block of a pure material is heated from 38 6 C to 52 3 C by the addition of 3 36 kJ of energy Calculate its specific heat in kJ kg C Your Answer

On the basis of the kinetic theory of gases when the absolute temperature is doubled the average kinetic energy of the gas molecules changes by a factor of 04 O 2 0 5 16 02

A certain metal has a specific heat c 0 21 cal g C and a mass m 25 6 g The initial temperature is T 34 6 C and the final temperature Tf 54 6 C The quantity of heat absorbed is 23 cal 0 23 cal 14 cal 110 cal 207 cal

8 What is the peak wavelength of a blackbody with a temperature of 12000 K 10 points

T What temperature in C is a blackbody whose emission spectrum peaks at 300 nm Submit Part B V A O Request Answer C What temperature in C is a blackbody whose emission spectrum peaks at 40 m

At what wavelength Am would the intensity of blackbody radiation be at a maximum when the blackbody is at 2900 K Express your answer in nanometers to two significant figures View Available Hint s VAE

A 3 4 cm diameter metal sphere is glowing red but a spectrum shows that its emission spectrum peaks at an infrared wavelength of 2 0 m Assume e 1 You may want to review Pages 1065 1067 Part A How much power does the sphere radiate Express your answer to two significant figures and include the appropriate

Life is good for only two things discove 9 The corpse of a famous math midnight in his mansion The Newton s Law of Cooling to d temperature was 98 6 F at th T t objects temperature A constant temperature

Two containers of the same substance have masses and temperatures as shown Which box has the larger thermal energy A Box A B Box B C They are the same D There s no way to tell OC OB O A Box A 100 g 0 C Box B 20 g 50 C

A picture window has dimensions of 1.77 m by 2.68 m and is made of glass 5.14 mm thick. On a winter day, the outside temperature is -20°C, while the inside temperature is a comfortable 19.5°C. At what rate is heat being lost through the window by conduction? kglass = 0.80 W/m.K Round your answer to 2 decimal places.

A 43-cm long cylindrical rod conducts 175 J/s from a furnace at 325°C to a container of boiling water under 1 atmosphere. Compute its diameter if it is made of steel (k = 50.2 W/m-K). Express your answer in cm. Round your answer to 2 decimal places.

A tungsten sphere (r = 1.41 cm) is needed to be maintained at 3314 K. The walls of the enclosure, where it is suspended within, are at 251 K. Ignoring the heat conduction along the supports, calculate the needed power input. The emissivity of tungsten is 0.350. Express your answer in kW. Round your answer to 2 decimal places.

A tungsten sphere (r = 1.08 cm) is needed to be maintained at 3249 K. The walls of the enclosure, where it is suspended within, are at 260 K. Ignoring the heat conduction along the supports, calculate the needed power input. The emissivity of tungsten is 0.350. Express your answer in kW.

Two rooms, each a cube 4 m per side, share a 10.9-cm thick brick wall. Because of a number of 100-W lightbulbs in one room, the air is at 24 deg C, while in the other room it is at 14 deg C. How many of the 100-W bulbs are needed to maintain the temperature difference across the wall? kbrick = 0.84 W/m.K Round your answer to 2 decimal places.

Two 99 sq cm plates which are both 2.21 mm thick are soldered together. Plate A is at 155°C while plate B is at 0°C. Considering the following thermal conductivities, what is the temperature at the soldered junction? k(a) = 43.74 W/m.K k(b) = 59.62 W/m.k Round your answer to 2 decimal places.

One end of an insulated metal rod is maintained at 100 deg C, and the other end is maintained at 0 deg C by an ice-water mixture. The rod is 74 cm long and has a cross-sectional area of 1.25 cm²? What is the thermal conductivity (W/m.K) of the rod if heat current is 4.97 W? Round your answer to 2 decimal places.

A 34-cm long cylindrical rod conducts 188 J/s from a furnace at 344°C to a container of boiling water under 1 atmosphere. Compute its diameter if it is made of steel (k=50.2 W/m K). Express your answer in cm. Round your answer to 2 decimal places.

If left untreated, which of these is the most likely outcome of a binge-eating disorder? O A.Obesity O B.Anorexia nervosa O C.Excessive muscle mass O D.Tooth decay

Two rooms, each a cube 4 m per side, share a 13.9-cm thick brick wall. Because of a number of 100-W lightbulbs in one room, the air is at 20 deg C, while in the other room it is at 9 deg C. How many of the 100-W bulbs are needed to maintain the temperature difference across the wall? Kprick = 0.84 W/m.K Round your answer to 2 decimal places.

A picture window has dimensions of 1.3 m by 2.28 m and is made of glass 5.62 mm thick. On a winter day, the outside temperature is -20°C, while the inside temperature is a comfortable 19.5°C. At what rate is heat being lost through the window by conduction? kglass = 0.80 W/m.K