Transmission of heat Questions and Answers

23 A body of length 1 m having cross sectional area 0 75 m has heat flow through it at the rate of 6000 J s The difference between two ends of conductor if K 200 J m K 1 is 40 C 100 C 1 20 C 3 80 C 2 4 onductivities 2

4 35 A rod of length with thermally insulated lateral surface and cross sectional area A consists of material whose heat conductivity coefficient varies with temperature as k a T where a is a constant The ends of the rod are kept at temperatures T and T T T Find the function 7 x where x is the distance from the end whose temperature is T and the heat flow density 2 2 Ans T x T T T q a l In T T

Four square pieces of insulation are available to cover an opening area 2A They are of different materials with conductivities K and K as shown and arranged as shown for case I and case II They are of same thickness and area A Find the correct option to ensure lesser heat flow K K K K Case I O Case Il O Case 1 O Equal heat flow O Unpredictable K K K K Case Il

4 similar rods which are thermally insulated are joined at point A If heat flows in from point B at rate of 1W and from point C at 3W inside flows out from D at 5W which relation is correct for temperature of these points A TA TE B TB Tc B C X E D C Tc TD D TB TE

A hollow spherical ball of inner radius a and outer radius 2a is made of a uniform material of constant thermal conductivity K The temperature within the ball is maintained at 2T and outside the ball it is T Find a the rate at which heat flows out of the ball in the steady state b the temperature at r 3a 2 where r is radial distance from the centre of shell Assume steady state condition AOL 0 2a a 2TO K T

A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K If the radius were halved and the temperature doubled the power radiated in watt would be NEET 2017 1 225 2 450 3 1000 4 1800

0 Certain quantity of water cools from 70 C to 60 in the first 5 minutes and to 54 C in the nex minutes The temperature of the surroundings i AIPMT 20 1 45 C 2 20 C 3 42 C 4 10 C

The top of the lake is frozen The air in contact with surface of lake is 20 C Then the maximum temperature of water in contact with lower surface ice will be 6 C 10 0 C C 273 C English

Example 22 13 A cylinder of radius R made of a material of conductivity K is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K The two ends of the combined system are maintained at two different temperatures There is no loss of heat across the cylindrical surface and the system is in steady state The effective thermal conductivity of the system is JEE 1998 a K K c K 3K 4 b K K K K d 3K K 4 Solution Let R and R be the thermal resistances of inner and outer portions Since temperature difference at both ends is same the resistances are in parallel Hence or bow 2R option is c Fig 22 16 1 RR R 1 R 1 KA KA 1 K R K 4 R K R K 3 R 1 1 1 ban K 3K 4 09 01 SS olgm 028 no

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

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 1 1 2 7 A 20 C 20 C B D C 90 c 2 7 2 O C

119 An ideal diatomic gas is slowly keeping pressure constant The work done by the gas is 1 Q Last 3 3Q 7 w 2 4 Q Q 7

having same cross section and length have been joined as shown The temperature of the junction of four rods will be 10 C 0 20 C 100 C 70 C 1 20 C 2 25 C 3 50 C 4 60 C

Zero Marks 0 In all other cases wall has two layer A and B each made of different material both the layers have the same thickness The thermal conductivity of the material A is twice that of B Under thermal equilibrium t fference across the wall B is 36 C The temperature difference across the wall A for the flow of heat through its thickness is in C

20 A wall has two layers A and B each made of different materials Both the layers have the same thickness The thermal conductivity of the material of A is twice that of B Under thermal equilibrium the temperature difference across the wall is 36 C The temperature difference across the layer A is A 6 C C 18 C B 12 C D 24 C 1

After heating two pieces of iron they are taken in dark room One of them appears red and another appears blue then 1 The temp of red piece will be more 3 The temp of both pieces will be same 2 The temp of blue piece will be more 4 Nothing can be said about their temp 10 12 watt cm K Temperature

1 A In The spectral emissive power of a black body at a temperature of 6000K is maximum at 5000 A If the is increased by 10 then the decrease in will be temperature 1 2 5 2 5 0 3 7 5 4 10 ission of energy by a unit area of a body is 10 watt and that of sun is 106 watt The emissive power of

Two identical calorimeters of negligible heat capacities are filled with two liquids A B whose densities are in the ratio 4 3 The ratio of times taken in cooling from 80 C to 75 C is 5 6 The ratio of their specific heats is 11 2 2 5 6 3 4 3 4 5 8 nives heat from a heated sphere placed at a distance r from it It is found that foil receives

1 6000K 2 5500K 3 580 The rate of a cooling of a heated solid sphere is R cal min If it is divided into two hemispheres the rate of cooling at the same temperature will become 1 1 25R cal min 2 1 5R cal min 3 1 75R cal min 4 2 5R cal min liquide A Band of same yolumes are in the ratio 3 2 1 They are allowed to cool in

4 32 5 C 1 16 5 C 2 22 5 C 3 28 5 C Which of the following surfaces will absorb maximum radiant energy 1 Black 2 Rough 3 Smooth white 4 Rough black incer of iron they are taken in dark room One of them appears red and anothe

Reflection and absorption coefficients of a given surface at 0 C for a fixed wavelength are 0 5 each At the same temperature and wavelength the transmission coefficient of surface will be 1 0 5 2 1 0 3 zero 4 in between zero and one from the centre of the sun to the

cal cm sec C and 0 016 cal cm sec C then the temperature of the junction is 1 40 C 2 60 3 100 C 4 50 C Two rods of copper and brass of same length and area of cross section are joined as shown One end is kept at 100 and the other at 0 C The temperature at the mid point will be

A long metallic bar is carrying heat from one of its ends to the other end under steady state The variation of temperature 8 along the length x of the bar from its hot end is best described by which of the following figures AIEEE 2009 1 2 3 4

The stove has a room temperature of 21 C until it is lit When lit the temperature of the stove rises by 9 C every minute a What is the temperature of the stove after being lit for 20 minutes b The meal has to be baked at a temperature of 318 C How many minutes does it take to heat the stove to the right temperatu

4 50 C in both the above cases The energy emitted per second by a black body at 1227 C is E If the temperature of the black body is increased 2727 C the energy emitted per second in terms of E is 1 16 E 2 E 3 4E 4 2E

m A compound slab is composed of two parallel layers of different material with thicknesses 3 cm and 2 cm The temperatures of the outer faces of the compound slab are maintained at 100 C and 0 C If conductivities are 0 036 cal cm sec C and 0 016 cal cm sec C then the temperature of the junction is 1 40 C 2 60 C 3 100 C 4 50 C of cross section are joined as shown One end is kept at 100 C

A cup of tea cools from 80 C to 60 C in one minute The ambient temperature is 30 C In cooling from 60 C to 50 C it will take 1 30 seconds 2 60 seconds 3 96 seconds 4 48 seconds 70 C to 60 C in 5 minutes The time needed by same liquid to cool from 60 C to 50 C will be

A liquid when heated in a copper vessel and when heated in a silver vessel the apparent coefficient of expansion is C and S respectively If coefficients of linear expansion of copper is A then the coefficient of linear expansion of silver is T3 TA L face a far safada fer farart qui fueran the facar quires A C S 3A 3 B C 3A S 3 C 3A S C 3 D C S 3A 3

A square is made of four rods of same material one of the diagonal of a square is at temperature difference 100 C then the temperature difference of second diagonal 100 Y 0 C 2 100 3 100 2 8 100 C

Two bodies A and B have thermal emissivities of 0 01 and 0 81 respectively The outer surface areas of the two bodies are the same The two bodies emit total radiant power at the same rate The wavelengths and 2 corresponding to maximum spectral radiancy in the radiation from A and B respectively differ by 1 00 m If the temperature of A is 5802K Find 2 0 01 0 81 and 3 A 31 00 m 5802K 2 fa A 1 5 10 m B 3 2 10 m C 5 10 m D 7 5 10 m Your Answ

Which of the following is more close to a black body Black board paint 2 Green leaves 3 Black holes 4 Red roses A black body is at a temperature of 2800 K The energy of radiation emitted by this object wi

d toy The power radiated by a black body is P and it radiates maximum energy at wavelength If the temperature of the black Zo body is now changed so that it radiates maximum energy at wavelength the power radiated by it becomes nP The NEET 2018 X3 256 81 value of n is 1 3 4 2 4 3 4 81 256

3 It can t be resolved at any tin 4 In begining it is seen most black and later on it can t be resolved What is the mode of heat transfer by which a hot cup of coffee looses most of its heat 2 convection 3 evaporation 4 radiation 1 condiction Which one of the following processes depends on gravity RPMT 2014 AIPMT 2000

Assuming the sun to have a spherical outer surface of radius r radiating like a black body at temperature t C the power received by a unit surface normal to the incident rays at a distance R from the center of the sun is Salan Constar 4 r t R 16 r ot 1 2 r t 273 4 R 3 R A black body is at 727 C It emits energy at a rate which is proprotional to r t 273 4 R S Ts Rs R

Two circular discs A and B with equal radii are blackened They are heated to same temperatur identical conditions What inference do you draw from their cooling curves 1 A and B have same specific heats magifin haat of B is less R 20 A B 8 9 2 Specific heat of A is less 4 Nothing can be said RPMT 2007

If the door of a refrigerator is kept open then which of the following is ture 1 Room is cooled 2 Room is heated 3 Room is either cooled or heated 4 Room is neither cooled nor heated 2078 C and 127 C It a

Two sample A and B are initially kept in the same state The sample A is expanded through an adiabatic process and the sample B through an isothermal process upto the same final volume The final pressures in A and B are p and Pa respectively PAPB 2 PA PB 3 P PB 4 The relation between p and p cannot be deduced Let T and T be the final temperature of the samples A and B respectively in the previous question then NT T 2 T T 3 T T IT cannot be deduced

Stress vs strain curve for the elastic tissue of the aorta the large tube vessel carrying blood from the heart will be stress is proportional to square of the strain for the elastic tissue of the aorta

56 A composite slab consists of two different materials having equal cross sectional area but lengths in the ratio 2 1 and thermal conductivity K and 3K respectively as shown in figure The equivalent thermal conductivity of slab is 1 3 9K 7 3K A K 2L 2 4 3K 3K 2 3K L

7 Figure shows a composite wall made of two walls A and B each of equal area and thickness Ratio of thermal conductivity of A and B is 3 2 Temperature of the common face is 1 30 C 3 35 C A B 1 40 C 20 C 2 32 C 4 37 5 C

A metallic rod of cross sectional area 9 0 cm and length 0 54 m with the surface insulated to prevent heat loss has one end immersed in boiling water and the other in ice water mixture The heat conducted through the rod melts the ice at the rate of 1 gm for every 35 sec Find the thermal conductivity in W m K of the rod Latent heat of fusion of ice 80 cal g J 4 2 J cal

NAU AW in a adiabatic process 3 AU AW in a adiabatic process 4 AU AW in a isothermal process If C and C denote the specific heats per unit mass of an ideal gas of molecular weight M where R is gas constant then AIPMT 2010 1 C C R M 2 C C R 3 C C R M 4 C C MR th of its original volume What is

molecule of the gas is m Which of the following gives the density 3 P KTV 1 P KT 2 Pm KT 4 mkT The temperature inside a refrigerator is t C and the room temperature is t C The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be NEET II 2016 1 4 273 1 1 4 1 1 1 273 2 3 L 273 4 4 1 t NEET II 2016 l of an ideal monoatomic gas undergoes a process described by the equation PV constant The heat

An ideal gas goes from state A to state B via three different processes as indic If Q Q Q indicate the heat a absorbed by the gas along the three processes and AU AU AU indicate the change in internal energy along the three processes respectively then AIPMT 2012 1 Q Q Q and AU AU AU 2 Q Q Q and AU AU AU 3 Q Q Q and AU AU AU O and Al ALL AU CAV

30 gm of ice at 14 C is added to 200 gm of water at 25 C Find the equilibrium temperature Take specific heat of ice 0 5 cal g C specific heat of water 1 cal g C and latent heat of ice 80 cal g

material and having the same cross section have Three rods made of the same as A been joined as shown in the figure Each rod is of the same length The left and right ends are kept at 0 C and 90 C respectively The temperature of junction of the three rods will be JEE 2001 a 45 C c 30 Cabeldo Solution Let 0 be the temperature of the junction say B Thermal resistance of all the three rods is equal Rate of heat flow through AB Rate of heat flow through CB Rate of heat flow through BD Solving this equation we get The correct option is b Here R Thermal resistance f heat flow b 60 C d 20 C H 0 C Temperature difference TD Thermal resistance R Fig 22 14 stomex3 sowo wif 90 8 90 0 0 0 D B R R R 0 C 0 0 60 C A BSS elama itssh AS schpen Fig 22 15 1 s 90 C 90 C 90 C 90 C

5 The temperature of inversion of a thermocouple is 620 C and the neutral temperature is 300 C What is the temperature of cold junction AIPMT Prelims 2005 1 20 C 2 320 C Pano 3 20 C 4 40 C

a 0 5 Am A substance cools from 75 C to 70 C in T minute from 70 C to 65 C in T minute and f 65 C to 60 C in T3 minute then a T T T c T T T3 b T T T d T T T pro at temperatures 20 C and 40 C When same mass of both of them is mixed of their specific beats

c 75 C d 0 C 9 A wall has two layers A and B each made of different materials The layer A is 10 cm thick an Bis 20 cm thick The thermal conductivity of A is thrice that of B Under thermal equilibriun temperature difference across the wall is 35 C The difference of temperature across the laye A is aguibu b 14 C a 30 C d 5 C c 8 75 C A wall has two lafiora ond Roach made of different C

The activation energy of a reaction can be determined from the slope of which of the following graph k vs T k vs 2 T