Transmission of heat Questions and Answers

5 Two spherical black bodies made of san material and with the same surface finish hat masses M and M and are at temperatur T and T If they are radiating the san power M1 M2 must be A T T C T T B T T D T T

H One end of a rod is maintained at a fixed temperature Tu while the other end is attached to a container having water of mass m at temperature T The thermal conductivity the cross sectional area and the length of the rod are k A and I respectively whereas the density and specific heat capacity of water are p and s respectively Find out the temperature of the water as a function of time Take T TH TH k A 1

14 Assertion The division are equally marked on the scale of AC ammeter Reason Heat produced is directly proportion to current 1 Point OOC if both Assertion and Reason are true and Reason is correct explanation of the Assertion if both Assertion and Reason are true but Reason is not correct explanation of Assertion if Assertion is true but Reason is false if both Assertion and Reason are false

39 The temperature of a body falls from 62 C to 39 50 C in 10 minutes If the temperature of the surroudings is 26 C the temperature in next 10 minutes will become 1 42 C 2 40 C 3 56 C 4 55 C 10 fz 62 C fr 50 C 26 C 8 1 42 C 2 40 C 3 56 C 4 55 C 10

I Molten magnesium is the most efficient and commonly used coolant in the nuclear reactor II Shut down position and critical stage occur during the operation of nuclear reactor SolveLancer Test a I is incorrect and II is correct b I is correct and II is incorrect c Both statements are correct d Both statements are incorrect

An open container holds ice of mass 0 505 kg at a temperature of 16 2 C The mass of the container can be ignored Heat is supplied to the container at the constant rate of 770 J minute The specific heat of ice to is 2100 J kg K and the heat of fusion for ice is 334 x 10 J kg Part A How much time tmelts passes before the ice starts to melt View Available Hint s tmelts Submit Part B VAE minutes From the time when the heating begins how much time trise does it take before the temperature begins to rise View Available Hint s

You are boiling pasta and absentmindedly grab a copper stirring spoon rather than your wooden spoon The copper spoon has a 25 mm x 1 2 mm rectangular cross section and the distance from the boiling water to your 35 C hand is 18 cm Part A How long does it take the spoon to transfer 25 J of energy to your hand Express your answer with the appropriate units A

An object with initial temperature 150 C is placed outside where the temperature is 35 C Its temperatures at 12 15 and 12 20 are 120 C and 90 C respectively a At what time was the object placed outside b When will its temperature be 40 C

A wire 3 00 m long and 0 450 mm in cross sectional area has a resistance of 38 3 at 20 0 C If its resistance increases to 38 8 at 28 0 C what is the temperature coefficient of resistivity C

Q2 25 July 2021 Shift 1 mathongo mathongo mathongo mathongo mathongo Two different metal bodies A and B of equal mass are heated at a uniform rate under similar mathongo mathong conditions The variation of temperature of the bodies is graphically represented as shown in the figure The ratio of specific heat capacities is mathongo Temp T C 150 120 90 60 30 1 B 2 3 4 5 6 7 8 mathongo mathongo mathongo mathonga mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathonga Time t s mathongo mathongo mathongo mathongo mathongo mathongo 1 2 3 mathongo mathongo mathongo mathongo mathongo mathongo 3 nathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo

3 2 n 1 p p 21 The efficiency of an ideal heat engine working Q 121 between the freezing point and boiling point of water is 1 26 8 3 6 25 4 1 n 1 p p 2 20 4 12 5 3 2 n 1 plp 4 1 n 1 Tage deri te gift 8 for at 1 26 8 3 6 25 2 20 4 12 5

5 The power radiated by a black body is P and it radiates maximum energy at wavelength If the temperature of the black body is now changed so that it radiates maximum 3 0 the power radiated by it 4 2018 energy at wavelength becomes nP The value of n is 256 81 a b 4 3 C 3 4 d 81 256

39 Two bottles A and B have radii R and R and B A B B A B heights h and h respectively with R 2R and h 2h These are filled with hot water at 60 C Consider that heat loss for the bottles takes place only from side surfaces If the time the water to cool down to 50 C is t and to for the bottles A and B respectively then t and to are B best related as a t t c t 4t b t 2tA B d t t 2

One end of a thermally insulated rod is kept at a temperature T and the other at T The rod is composed of two sections of lengths and thermal conductivities K and K respectively The temperature at the interface of the two sections is T 41 2 T O K T K T K K 8 O K 1 T K 2 T2 K l K 8 O K12T1 K 1T2 K182 K 81 O K l T K 2T2 K K22 K K

70 Three copper blocks of masses M M and M3 kg respectively are brought into thermal contact till they reach equilibrium Before contact they were at temperatures T T and T3 T T2 T3 Assuming there is no heat loss to the surroundings the equilibrium temperature T is s is specific heat of copper a T T T T3 3 b T M T M T M3T3 M M M3 c T d T 2 M T M T M3T3 3 M M M3 MTs M T s M T3s M M M3 2200 80 140 AB 600 1200 CP 8400 3600 Bu

Here is given work done on the gas means positive wor k W 8J not 8J but when put 8J then answer is com e otherwise not why sir ma am please explain it 3 64 81 4 8 27 V 3 3 2 n In a thermodynamic process pressure of fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas If initial internal energy of the gas was 40 J what will be final internal energy 1 18 J 2 28 J 3 52 J 4 32 J Choose the correct statement 4Q 4U AW AV AQ AW 40 0f U

A thermally insulated vessel is divided into two parts by a heat insulating massless piston which cann in the vessel without friction The left part of vessel contains 1 mole of an ideal monoatomic gas and part is empty The piston is connected to the right wall of vessel through a spring whose length in freest is equal to the length of the vessel Heat capacity of the system is found to be nR Find n Heat capa of the vessel piston and spring are negligible k 00000000

A compound bar 2 0 m long is constructed of a solid steel core 1 0 cm in diameter surrounded by a copper casing whose outside diameter is 2 0 cm The outer surface of the bar is thermally insulated One end is maintained at 100 C and the other end is at 0 0 C Find the total heat transfer in the bar

s of um rth S 1 6 A rubber of volume 2000 cc is alternately subjected to tension and released The figure shows the stress strain curve of rubber Each curve is a quadrant of an ellipse The amount of energy lost as heat per cycle per unit volume will be 4 Stress x 102 Nm 2 32 2 T 3 2 4 6 8 10 Strain 1 1 16 10 3 2 1 8 10 3 J x8x1 4 J

Six solid rods of equal length I and area section A are connected as shown Out of six rods three are made up of material x and other three of material y The thermal conductivity of x is twice that of y If end A and end D are kept at 60 C and 10 C respectively then which of the following statement s is are correct AQATTIT X B y X E X 1 Temperature at B temperature at D 2 Temperature at C 24 3 C 3 Temperature at C temperature at E

24 70 cal of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30 C to 35 C The amount of heat required in calories to raise the temperature of the same gas through the same range 30 C 35 C at constant volume is a 30 cal c 40 cal b 50 cal d 90 cal

neet prep 18 Two bodies A and B have thermal emissivities of and 0 81 respectively The outer surface areas of the bodies are the same The two bodies emit total rad power at the same rate The wavelength corresponding to maximum spectral radiancy in radiation from B is shifted from the waveler corresponding to maximum spectral radiancy in radiation from A by 1 00 pm If the temperature of 5802 K Mini Test 7 a The temperature of B is 1964 K b An 1 5 m Quote ep 11604 K

FL0023 24 Two wires of the same length and material but different radii r and r are suspended from a rigid support both carry the same load at the lower end The ratio of the stress developed in the second wire to that developed in the first wire is 5 2 3 1 1 2 4 4 2 FL0024

1 8 A metal plate 4 mm thick has a temperature difference of 32 C between its faces It transmits 200 kcal h through an area of 5 cm Thermal conductivity of the material is AIIMS 2010 a 58 33 W m C b 33 58 W m C c 5 104 W m C d None of these For cooking the food which of the following type of utensil is most suitable ISCRA 1998

1 61A Find various orders of Bragg s b Carbon is allowed to diffuse through a steel plate 10 mm thick The concentrations of carbon at the two faces are 0 85 and 0 40 kg m which are maintained constant If the preexponential and activation energy are 6 2 x 10 7 and 80 000 J mol respectively compute the temperature at which the diffusion flux is 6 3 x 10 10 Kg m s 2

Two rods of same material have same length and area The heat AQ flows through them for 12 minutes when they are jointed in series If now both the rods are joined in parallel then the same amount of heat AQ will flow in 1 24 min 2 3 min 3 12 min 4 6 min

30 Four identical rods of same material have been joined to make it a X shape structure If their ends are maintained at temperatures as shown in the figure then temperature at junction will be 60 C 40 C 60 x 1 20 C 3 70 E 100 C 0 C 2 50 C 4 40 C

18 A tungsten lamp at a temperature of 3000 K has surface area of 0 3 cm If the lamp has emissivity of 0 4 the rate of heat radiated is NCERT Pg 295 1 40 W 3 90 W 2 50 W 4 55 W

2 4 55 W 1 40 W 3 90 W 9 The amount of radiations emitted by a perfectly black body is proportional to NCERT Pg 295 1 Temperature on ideal gas scale 2 Fourth power of temperature on ide nas scale

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

Two different metal bodies A and B of equal mass are heated at a uniform rate under similar conditions The variation of temperature of the bodies is graphically represented as shown in the figure The ratio of specific heat capacities is 1 Temp C 00 m 150 120 28881 90 60 30 1 2 3 4 5 6 7 8 Time s mathongo motharigo 2

A thermodynamic system is taken from original state to another intermediate state by linear process shown in diagram Its volume is then reduced to original volume from B to C by an isobaric process What is total work done by gas from A to B to C NCERT Pg 322 tion Pressure N m 191 600 A 400 C 1 500 J B E F volume m 5 0 1 0 2 400 J 4 2000 J

n 35 A cylindrical conductor is connected across a battery and when a steady state is reached temperature of the conductor exceeds the ambient temperature by A0 16 C If the length of the conductor is reduced to 0 8 times by cutting off extra length and other conditions are kept unaltered by what amount will the temperature of the conductor change

A body cools from 5T to 2T in 5 minutes The room temperature is T Assume that newton s law of cooling is applicable The temperature of the body at the end of next 5 minutes will be 7 3 2T 3 5T 4

A uniform wooden plank cuboid is floating on water is tied to the bottom of the pool such that in static equilibrium the diagonal plane of symmetry of its vertical cross section coincides with the level surface of water as shown in figure The specific gravity of the wood is reciprocal of p The value of p is A GROUP PRONE COKSD

A circular conducting coil of radius 1 m is being heated by the change of magnetic field B passing perpendicular to the plane in which the coil is laid The resistance of the coil is 2 2 The magnetic field is slowly switched off such that its magnitude changes in time as B 4 10 T 1 T t 100 The energy dissipated by the coil before the magnetic field is switched off completely is E mJ

The temperature of the two outer surfaces of a 15 composite slab consising 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 A T T K T K f with f which equal to X 1 1 3 3 Two T 2K T 2 D 12 13 ng proce 16 van eigen af at a f K 3x3 4x aft 14 T T tereftaten 1 1 K 3 A T T K X 3 T fa fa 2K T 112713 mbaff van Am at fir

A steel measuring tape and a copper rod are a heir true length at room temperature Their therma coefficient of linear expansion are a and a respectively However measurement of copper rod length by steel tape is shown as Lo at a temperature 40 higher than room temperature The correct length of the copper rod at room temperature is 4 I 00

Consider two insulating sheets with thermal resistances R and R as shown The temperature 0 is R 1 3 0 0 0 R R R1 R2 01 0 01 02 R R2 R R 0 2 4 R 0 0 R 0 R2 R R 01 R 0 R R R

black rectangular surface of area A emits energy E per second at 27 C If length and breadt rd of initial value and temperature is raised to 327 C then energy emitted pe reduced to 3 cond becomes 4E 9 B E 9 C jence 16E 9 2E D 222 ience

rdinary bodies A and B radiate maximum energy with wavelength difference 4 m The Osolute temperature of body A is 3 times that of B The diates maximum energy is wavelength at which body B wavelength D 6 m A 4 m B 8 m C 12 m Cath

Q 14 Let us assume that sun radiates like a black body with surface temperature at T 6000 K and earth absorbs S radiations coming from sun only If both earth and sun are considered as perfect sphere with distance between centre of earth and centre to sun to be 200 times the radius of sun The temperature of surface of earth in steady state is found to be 100C K and then C is Assume radiations incident on earth to be almost parallel Answer Rate this question

3 A steel tape is calibrated at 25 C On a cold day when the temperature is 0 C then the percentage error in the tape is Given a for steel is 1 2 x 10 6 C 1 1 0 01 3 0 03 closed 2 0 02 4 0 04 system receives 250 kir heat

200 gram ice at 20 C is mixed with 100 gram water at 60 C If specific heat of ice is 0 5 calorie gram K and that of water is 1 calorie gram K then final temperature of the resulting mixture would be assume no heat loss to the surroundings 1 0 C 2 10 3 5 C 4 15 C

About black body radiation which one of the following is WRONG statement A For all wavelengths intensity is same B All wavelengths are emitted by a black body C For longer wavelengths intensity is less D

Two spherical black bodies made of same material and wi th the same surface finish have masses M1 and M2 and are at temperatures T1 and T2 If they are r adiating the same power 1 M2 M must be Ans T2 T1 6

2 Two rods of electrical conductivities K and K ar connected as shown in the figure Find the equivalent electrical conductivity of the system A 3 OI RIK K 2R V 1 K K K 2K 4 K 2 4 10 B K 3K 4 4K K 4

Rate of radiation by a black body is R at temperature T Another body has same area but emissivity is 0 2 and temperature 3T Its rate of radiation is A B C D 8 1 R 16 2 R 24 3 R 32 4 R

A closed cubical box is made of perfectly insulating material The only way for the heat to enter or leave is through two solid cylindrical plugs each of cross sectional area 12cm and length 8 cm The 100 C material of the plugs has K 2 Wm K A source S of energy generating 13 W is kept inside the box The outside temperatures on the two plugs are maintained at 100 C and 40 C respectively Find the equilibrium temperature in C of the inner surface assuming it to be same for all points on the inner surface S 40 C

Two identical objects A and B emissivity e and e are placed in an enclosure Temperature of body A B and enclosure are same and constant Heat emitted by body A is not equal to heat emitted by body B Heat absorbed by body A is not equal to heat absorbed by body B If eA eB body A absorbs more heat than body B If eA eB body A emits less heat than body B