Transmission of heat Questions and Answers

I have asked this question previously However no satisfac tory response was provided My straightforward question is that why in question no 29 we are using dT dt 1 R and in question 40 we are saying dT dt is independent of radius i e option number 4 Reque st you to explain it properly this time as I can t ask the sa me question again again 29 Two metal spheres of same material have diameter in the ratio of 1 2 The ratio of their rates of cooling is 1 4 1 2 2 1 3 1 2 4 1 4 40 A very thin metallic shell of radius r is heated to temperature T and then allowed to cool The rate of cooling of shell is proportional to 1 rT 3 2 2 4 r Asked by 2525299 aesl id Standard XI Stream NEET Jul 27 2021 at 7 12 PM Add your responses Type Text Type your answer here OR you can upload an lattachment from the option below

An ice box is built of wood 1 75 cm and fiber of 2 cm thickness as shown If the temperature of inner surface of fiber is 0 C and that of outer surface of wood is 12 C what is the temperature in C of interface Given K of wood 0 0006 units and that of fiber is 0 00012 units ice 0 C Correct answer 10 21 fiber wood 12 C

2 23 A block of metal is heated directly by dissipating power in the internal resistance of block Because of temperature rise the with resistance increases exponentially time and is given by R t 0 5 e2t where t is in second The block is connected across a 110 V source and dissipates 7644 J heat energy over a certain period of time This period of time is 10 sec take In M

3 5 kg lead ball is dropped into a 2 6 L insulated il of water initially at 20 0 C Part A If the final temperature of the water le combination is 26 9 C what was the temperature of the lead ball Express your answer using two

The temperature T versus time t graphs of two bodies X and Y with equal surface areas are shown in the figure If the emissivity and the absorptivity of X and Y are Ex E and Ax A respectively then T A Ex Ey Ax Ay C Ex Ey Ax Ay B Ex Ey A Ay D Ex Ey Ax Ay y X t 0 t 200

A If 20 grams of water at 20 C is supplie 20 Cal of heat energy then temperature of water is ie A 20 C B 21 C C 40 C The temperature of a substance D 19 C is 27 C

Dear sir mam I have a doubt in physics Sir mam my doubt is a vessel contains 100 gram water at 10 degree Celsius at 42 ohms resistance wire is immersed in it and a current of 2 0 ampere is passed through it for 5 minutes if the heat capacity of The vessel is 50 calorie per degree Celsius then find the increase in the water temperature Sir mam I request you to please clear my doubt Sir plaaso oxplain the answor

3 1 4 12 80 gm of water at 30 C is poured on a large block of ice at 0 C The mass of ice that melts is 1 30 gm 2 80 gm 3 4 150 gm 10 C into steam at 100 C is 1600 gm

3 1 16 C 3 Latent heat of ice is 80 cal gm A man melts 60 gm of ice by chewing in 1 minute His power 1 4800 W 2 336 W 3 1 33 W 4 0 75 W Dolhi 110005

A jug of buttermilk is set to cool on a front porch where the temperature is 0 C The jug was originally at 90 C If the buttermilk has cooled to 45 C after 30 minutes after how many minutes will the jug be at 9 C The jug of buttermilk will be at 9 C after n minutes Round the final answer to the nearest whole number as needed Round all intermediate values to six decimal places as needed

Gasoline has an enthalpy of combustion 24000 kJ gallon When gasoline burns in an automobile engine approximately 30 of the energy released is used to produce mechanical work The remainder is lost as heat transfer to the engine s cooling system As a start on estimating how much heat transfer is required calculate what mass of water could be heated rom 25 C to 75 C by the combustion of 1 0 gallon of gasoline in an automobile Given C H O 4 18 J g C a 34 45 kg d 224 kg b 80 383 kg c 22 kg

A uniform rod of cross sectional area A 0 2 cm is bent to form a squar of side 1 10 cm The ends A B and C of the square are maintained at 100 C 40 C and 0 C respectively If the thermal conductivity of the material of the rod is k 385 W m C and assuming that the rods are in steady state then for this situation the CORRECT statements are neglect energy losses due to radiation and convection B A 100 C D 40 C 0 C A Net rate of heat supplied by the reservoir at A is 8 47 J s B Temperature of D is less than 0 C C Temperature of D is less than 100 C D Heat current from B to C is 3 08 J s

4 Six identical conducting rods are joined as shown in figure A 200 C B 1 120 C 3 140 C C Points A and Dare maintained at temperatures 200 C and 20 C respectively The temperature of junction B will be D 20 C 2 100 C 4 80 C

A highly thin conducting spherical shell of radius R is completely filled with water at 0 C Outside surrounding temperature is T C Latent heat of fusion of water is L and thermal conductivity of ice is Ke Assume heat is flowing symmetrically in radial direction Choose the CORRECT option s Density of water is p Neglect the expansion of water on freezing water at 0 C Highly conducting thin shell ice Surrounding at T C A Time in which complete water will freeze is given by b Time in which complete water will freeze is given by PoL R 6KTo ice d Total heat released by water in freezing is given by PoL R ice 0 PL R C Time in which thickness of ice will become is given by 12K To 47 PLR 3

Power radiated by a perfectly black body is Po and wavelength corresponding to maximum energy is o On changing temperature the wavelength corresponding to maximum energy is increased by Now the power radiated by the body will be 20 200 O 2 P 3 4P 9

The temperature of a metal ingot is 60 C above room temperature right now Twenty minutes ago it was 75 C above room temperature a How far above room temperature will the ingot be 20 minutes from now b How far above room temperature will the ingot be 2 hours from now c When will the ingot be 10 C above room temperature a 20 minutes from now the ignot will be about C above room temperature Round to the nearest degree as needed wwwww

The graph shown in the figure represent change i he temperature of 5 kg of a substance as it abosrb eat at a constant rate of 42 kJ min The later eat of vapourazation of the substance is Temperature FC 700 175 150 125 100 50 24 050 15 20 25 30 35 10 15 50 time min 1 630 kJ kg 3 84 kJ kg 2 126 kJ kg 4 12 6 kJ kg

Three discs A B and C having radii 2m 4m and 6m respectively are coated with carbon black on their outer surfaces The wavelengths corresponding to maximum intensity are 300 nm 400 nm and 500 nm respectively The power radiated by them are Qa Qb and Qc respectively Question Type Single Correct Type 1 Qa is maximum 2 Qb is maximum 3 Qc is maximum

A point source of power P is placed on the axis of a thin hemispherical shell as shown The shell has a radius of 3m and behaves like a perfect black body If the steady state temperature of shell is T Find T4 after rounding off Take P 2400T W o stefan s const P 4m 3m

QA metal bar of length I is well lagged with some non conducting material to prevent losses of heat from its surface and the two ends are maintained at steady temperature 0 and 02 with 0102 then in the steady state the temperature of a section of the bar at distance X from the hot end varies as shown in the graph 0 0 0 1 0 0 0 3 0 0 0 2 0 00 4 X

The ends of a long bar are maintained at different temperatures and there is no loss of heat from the sides of the bar due to conduction or radiation The graph of temperature against distance of the bar when it has attained steady state is shown here The graph shows Temperature Distance from hot end

6 Three conducting rods of same material and cross section are shown in figure Temperatures of A D and C are maintained at 20 C 90 C and 0 C The ratio of lengths of BD and BC if there is no heat flow in AB is a 2 7 c 9 2 b b 7 2 A B D d 2 9

13 A copper rod and a steel rod of equal cross sections and lengths L are joined side by side and connected between two heat baths as shown in the figure T 3 copper 9 T T X 0 x 2L If heat flows through them from x 0 to x 21 at a steady rate and conductivities of the metals sterl are K K K K then the temperature varies as convection and radiation are negligible x 0 x 2L steel x L x 2 L 2L mettentr n L 13 L e aid m Rica y qu ma fanger se Heat baths 21 X K vied 1 3 T 9 x 0 copper K K V T T el L xx steell x 2L K at anvera ufada 8 X L x 2 L2L x 2L 21 x

The given indi diagram shows variation of pressure with volume when a thermodynamical system is taken from state A to state B During the process P A 0 0 B V 1 The system is cooled 2 The system is heated 3 The system heated first and then cooled stom oled first and then heated

The specific heat of a substance varia temperature is s 0 2 0 14 0 0 cal g C The heat required to rai temperature of 2g of substance from 15 C will be A 24 cal 82 cal et B 56 cal D 100 cal

14 A sphere and cube made of same material and having same surface area are heated to the same temperature and kept in the same surrounding The ratio of their initial rates of cooling will be TU 1 1 2 E TC TC 1 3 1 4 73 1

The ends of a long bar are maintain different temperatures and there is no loss of heat from the sides of the bar due to conduction or radiation The graph of temperature against distance of the bar when it has attained steady state is shown here The graph shows Temperature Distance from hot end i the temperature gradient is not uniform ii the bar has uniform cross sectional area iii the cross sectional area of the bar increases as the distance from the hot end increases iv the cross sectional area of the bar decreases as the distance from the hot end increases 1 i ii 2 i iii

The graph between two temperature scales A B is shown between upper fixed point and lower fixed point There are 150 divisions on scale A and 100 divisions on scale B Then relationship for conversion between two scales is given by Temp A 180 1 3 At 1000 of TA 180 TB 100 150 tA 180 LA 2 4 At 150 Temp B TA 30 tB 150 100 tB 40 ta tA

The temperature of the two outer surfaces of a composite slab consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x respectively are T and T T T The rate of heat transfer through the slab in a steady state is f with f which equal to A T T K X T K 2K T

hreerods of destiest ares of cross section and made from the same metal form the sides of an isoscelas ang ABC gargle st B The poets And Bac maintained at semperatures and 2 respectively In the stody state the bamperature of the point C T Amuring that only heat conduction takes place ogcalto A B C D in E VITA Amargos de met ADC 1 2 1 3 Your Answer Steady state f 2 1 1 2 2 1 1 13 2 1 m T T

A hemispherical bowl of radius R is filled with water and is cooling due to convection in atmosphere If its initial rate of cooling is de find the rate of cooling when the height of the water in the bowl is R 2 A B 2 dt 1 de C 1 de 2 dt 3 de D 3 de 4 dt

A highly thin conducting spherical shell of radius Ro is completely filled with water at 0 C Outside surrounding temperature is To C Latent heat of fusion of water is Lo and thermal conductivity of ice is Kice Assume heat is flowing symmetrically in radial direction Choose the CORRECT option s Density of water is po Neglect the expansion of water on freezing D Time in which complete water will freeze is given by Time in which complete water will freeze is given by Ro 2 Time in which thickness of ice will become Water at 0 C Highly conducting thin shell POLOR 6Kice To POLOR 4Kice To is given by POLOR 12Kice To Surrounding at T C

cal pipe of length 10 cm has inner radius 3 cm and outer radius r2 12 cm The temperature T1 difference between the inner and outer layer of cylindrical pipe is 100 C and the thermal conductivity of cylindrical pipe is 150 W m C Find the rate of heat transfered in kW between inner and outer layers Take In 2 0 693 A 3 4 B 6 8 C 10 D 13 6 11 12 Solution B

Figure shows two reservoirs containing two liquids of masses 4 m and 2 m and their specific heat capacities are s and 2s respectively Their initial temperatures are 47 and 7 respectively The containers are joined by a conducting rod of thermal conductivity K length 7 and cross section area A Specific heat capacity of the rod i negligible 4m S 4To P d kg A 2m 25 To The temperature of mid point P of the rod during the flow of heat A is always constant B Decreases

Consider a sphere of radius R with power source inside it The power of source is P In steady state temperature of surface of the sphere is To The sphere is now covered with a spherical shell of radius 2R Assume that no radiation are incident from any side and all surfaces are black bodies Select the correct alternative s G Power of source is 4n0T40R Power of source is noT4R Temperature of outer spherical shell in steady state is To 2

The power radiated by a black body is P and it radiates maximum energy around the wavelength Ao If the temperature of the black body is now changed so that it 3 radiates maximum energy around wavelength 4 power radiated by it will increase by a factor of 314 256 81 91 13 49 20 the

A vessel is divided into two parts A and B by a fixed partition The walls of the vessel and the partition are made of a perfect heat insulating material There is a hole in the partition which can be opened and closed Initially the hole is kept closed an ideal gas is filled in the part A and the part B is evacuated Now the hole is opened for a short time and then closed as a result some of the gas enters the part B Now the hole is again opened and gas is allowed to flow through the hole until net flow of the gas through the hole ceases How does the temperature of the gas change during the first and the second opening of the hole a During both the first and the second openings the temperature decreases b During the first opening the temperature remains constant but during the second opening the temperature decreases c During the first opening the temperature remains constant but during the second opening the temperature increases During both the first and the second openings the temperature remains constant A

A black body calorimeter filled with hot water cools from 60 C to 50 C in 4 minutes and 40 C to 30 C in 8 minutes The approximate temperature of surrounding is use average method 10 C 15 C 20 C 30 C

Questions 28 and 29 are based on the following physical situation A hollow cylinder made of a thermally insulating material is equipped with a horizontal piston P of mass m and area A The piston is also made of a thermally insulating material There is no friction between inner surface of the cylinder and the piston Above the piston a liquid of density p is filled up to brim of the cylinder The piston is supported at the position shown due to pressure of an ideal gas filled in the lower portion of the cylinder Number of moles of the gas is n atmospheric pressure is po and initial temperature of the gas is To The heater H is switched on 28 Work done by the gas on the piston is a pgh A mgh PhA 0 5pgh A mgh 29 Final temperature of the gas is Po pgh Po PA pghA mg nA mo a 27 s 27 b pohA pgh A mgh d 0 5 p hA pgh A mgh b 27 21 Po Po pgh PA mg PA pghA mg h P H oooooo

Heat is conducted across a composite block of two slabs of thickness dand 2d Their thermal conductivities are 2k and k respectively All the heat entering the face AB leaves from the face CD The temperature in C of the junction EF of the two slabs is d 2d A 100 C B 20 50 60 2K E4 F K C D 0 C

The total power emitted by a spherical blackbody of radius R at a temperature T is P Let P be the total power emitted by another spherical blackbody of radius R 3 kept at temperature 2T The ratio P P is a 0 25 b 0 62 c 0 82 d 0 56

Two vessels having equal volume contains molecular hydrogen at one atmosphere and helium at two atmospher s respectively If both samples are at the same temperature the mean velocity of hydrogen molecules is A B C Equal to that of helium Twice that of helium Half that of helium

A particle is in a cubic box with infinitely hard walls whose edges are L long Fig 5 18 The wave functions of the particle are given by Asin n X L n my sin L sin 11 w2 L 1 2 3 n 1 2 3 n 1 2 3 Find the value of the normalization constant 4

When a body is placed in surroundings at a constant temperature of 20 C and heated by a 10 W heater its temperature remains constant at 40 C If the temperature of the body is now raised from 20 C to 80 C in 5 minutes at a uniform rate the total heat it will lose to the surroundings will be A 3000 J C 4500 J B 3600 J D 5400 J

temperature An object kept in a large room having air of 25 C takes 12 minutes to cool from 80 to 70 C The time taken to cool for the same object from 70 to 60 C would be nearly 2 12 min 1 15 1 10 min 121 20

pond of surface area A containing water density p specific heat capacity s is located in a region where the outside air temperature is at a steady value of 26 C The thickness of the frozen ice layer in this pond at a certain instant is x Taking the thermal conductivity of ice as K and its specific latent heat of fusion as L the rate of increase of the thickness of ice layer at this instant would be given by 1 26K pr L 4s 2 26K px L 3 26K pxL 4 26K pr L 4s

SZ 180 250 cal Heat required to convert 10 g of ice at 10 C to water at 20 C is 2916 cal 850 cal Mark for Review 1050 cal hr min

Three identical rods are joined together as shown in the figure Temperatures are indicated The temperature at the junction is 10 C 21 C 70 3 C 30 C 11 20 C 40 C

them The temperature difference between a body and surrounding changes from 20 C to 10 C in 5 minute How long will it take to change the difference from 10 C to 5 C assuming Newton s law of cooling

4 A glass tube sealed at top end is inverted in mercury reservoir such that top end is at 76cm from free surface of mercury in reservoir Amount of monoatomic gas trapped in tube is 0 12 moles Now temperature of trapped air mercury and surroundings is increased very slowly by 2K Find Heat transferred to gas In Joule Given gas constant R 8 31 J mol k Atmospheric pressure pressure 76 cm of mercury Ignore effect of surface tension and any expansion in tube and mercury FEE