Transmission of heat Questions and Answers

39 40 in further 10 minutes it will cool from 38 C to A 36 C 8 36 4 C C 37 C The temperature of the body in C denoted by the variation of versus time t is best denoted as A C 40 C AC 8 D a C 10 D 37 5 C When the body temperature has reached 38 C it is heated again so that it reaches to 40 C in 10 minutes The total heat required from a heater by the body is

The work function of a photosensitive material 4 0 eV The longest wavelength of light that ca cause photon emission from the substance approximately NEET 2019 Odish 1 310 nm 3 966 nm 2 3100 nm 4 31 nm

A system of rods is assembled such that each rod has a length I and cross sectional area S The mode of heat transfer is conduction and the system is in steady state The temperature of the junction A is T and that of C is 2T Then the coefficient of therma conductivity values of the rods is as shown in figure RAMAY A Temperature of the junction B is 1 6T B Temperature of the junction D is 1 4T C The rate of heat flow along BD is D The rate of heat flow along BD is 1 KTS 51 21 KTS 5 1 AYATHE

Two liquids A and B are at temperature of 75 C and 15 C Their masses are in the ratio of 2 3 and their specific heats in the ratio 3 4 If these two liquids are mixed then the resulting temperature will be Question Type Single Correct Type 1 2 3 4 90 C 70 C 35 C 60 C

The filament of a light bulb has surface area 64 mm The filament can be considered as a black body at temperature 2500 K emitting radiation like a point source At night the light bulb is observed from a distance of 10 m Assume light detector to be circular with radius r 10 3 m Then Take o 5 67 x 10 Wm K Wien s displacement constant 2 90 x 10 m K Planck constant 6 63 x 10 Js speed of light in vacuum 3 00 x 10 m s assume detector absorbs all the radiation incident on it and point source filament lie on the axis of detector A Power radiated by the filament is in the range 642 W to 645 W B Radiated power entering into detector is in the range of 34 42 W tp 34 52 W The wavelength corresponding to the maximum intensity of light is 1160 nm D Taking the average wavelength of emitted radiation to be 1740 nm the total number of photons entering per second into detector is in the range 3 1 x 10 to 3 2 10

Two spheres A and B have the same radii but the heat capacity of A is greater than that of B The surfaces of both are painted black They are heated to the same temperature and allowed to cool in vacuum Then 1 A cools faster than B 2 both A and B cool at the same rate 3 at any temperature the ratio of their rates of cooling is a constant 4 B cools faster than A

A thermocouple of negligible resistance produces an e m f of 40 V C in the linear range of temperature A galvanometer of resistance 10 ohm whose sensitivity is 1 A div is employed with the thermocouple The smallest value of temperature difference that can be detected by the system will be a 0 25 C c 1 C 7 b 0 5 C d 0 1 C Charge q is uniformly spread on a thin ring of radius R The ring rotates about its axis with a uniform frequency fHz

8 Two identical bodies are made of a material for which the heat capacity increases with temperature One of these is at 100 C while the other one is at 0 C If the two bodies are brought into contact then assuming no heat loss the final common temperature is 2016 II a Less than 50 C but greater than 0 C b 0 C c 50 C d More than 50 C

Consider a sphere of radius R with a power source inside it The power of source is P In steady state temperature of surface of the sphere is T The sphere is now covered with a spherical shell of radius 2R Assume that no radiations are incident from out side all surfaces are black body Select the correct alternatives A Power of the source is 4no TR 5 122 1 1 2 C Temperature of outer spherical shell in steady state is D Temperature of inner sphere after covering is To B Temperature of inner sphere after covering is

Thermocouples are used to measure temperature in the linear parts of the emf versus temperature graph with cold junction at 0 C The thermo electric power of Pt Ni thermocouple are and 20 micro volt per C respectively What will be the magnitudes of emfs of the thermocouple when the cold junction is at 0 C and the hot junction is at 100 C B 2 mV D 1 6 mV A 4 mV C 3 2 mV hlar

Three very large plates of the same area are kept parallel and close to each other They are considered as ideal black surfaces and have very high thermal conductivity The first and third plates are maintained at temperatures 27 and 3T respectively The temperature of the middle plate under steady state condition is A B C 65 4 T 27 4 T 27 4 T Correct Answer

The energy transferred in 1 hour by conduction through a concrete wall 2 m high 3 65 m long and 0 2m thick if one side of the wall is held at 20 C and the other side is at 5 C is Thermal conductivity of concrete is 1 3 W m C 1 722 2 2 2 6 x 106 J 3 8468 4 8 46 10

For a given plate the coefficient of absorption is 0 60 and coefficient of transmission is 0 1 When calories of heat is incident on the plate the quantity of heat reflected from the plate is 2 100 cal 4 300 cal 1 600 cal 3 700 cal

Ice starts forming in a lake where the water is at 0 C and the ambient temperature is 10 C If the time taken for 1 cm of ice to be formed is 7 hours then the time taken for the thickness of ice to change from 1 cm to 2 cm is A B D 7 hours 14 hours 10 5 hours 21 hours

An electric water heater has a resistance of 12 ohms and is operated from 220 volt power line If no heat escapes from it how much time is required to raise the temperature of 40 Kg of water from 16 Cto 18 C A 63 3 sec C 83 3 sec B 73 3 sec D 93 3 sec

An engine operates between 2100 K and 700 K Its actual efficiency is 40 What percentage of its maximum possible efficiency is this Question Type Single Correct Type 1 2 40 60

A black body radiates maximum energy at wavelength 2 and its emissive power is E Now due to change in temperature of that body it radiates maximum energy at wavelength 2 At radiat hat temperature emissive power is 3 A 81E 16 B 91E 16 C 54E 16 D 27E 16

Please explain 15 A long metallic bar is carrying heat from one of its ends to the other end under steady state The variation of temperature 0 along the length x of the bar from its hot end is best described by which of the following graphs 1 3 X 2 4 X

A ring consisting of two parts ADB and ACB of same conductivity k carries an amount of heat H The ADB part is now replaced with another metal keeping the temperatures T and T constant The heat carried increases to 2H What should be the conductivity of 3 the new ADB part Given C 73 D 0 K O2k ACB ADB

Find the change in the entropy in the following process 100 gm of ice at 0 C melts when dropped in a bucket of water at 50 C Assume temperature of water does not change BHU Med 2000 a 4 5 cal K b 4 5 cal K

A window has dimensions of 1 05 m by 2 4 m and is made of glass 7 75 mm thick On a winter day the outside temperature is 25 C while the inside temperature is a comfortable at 18 C k of glass 0 135W m K 1 5 1 5 2 5marks Calculate the following a the area of the window in square metres b the temperature gradient AT Ax in kelvin metre c the rate of heat lost through the window by conduction in watts metre kelvin

B A heat pump can use a maximum of 2 5 kW power for maintaining a house at 20 C during winter The rate of heat transfer from the roof and walls is 3300 kJ h per degree temperature difference between inside and outside The COP is 60 of a reversible heat pump Determine the minimum outside temperature for which the heat pump can meet the heating requirements of the house

An automobile vehicle of 1500 kg mass is running at a speed of 60 km hr The brakes are applied and the vehicle is brought to rest Calculate the rise in the temperature of the brakes if their mass is 15 kg Take specific heat of the material of brakes 0 46 kJ kg K

Three rods A B and C of thermal conductivities K 2K and 4K and equal cross sectional areas and lengths 21 t and t respectively are connected as shown in the figure If the ends of the rods are maintained at temperatures 100 C 50 C and 0 C respectively then the temperature 9 of the junction is find x 100 C

hree superconducting thin plates are given where temperature of plates at steady state are T T T3 espectively as shown in figure If each side of plate can absorb only 80 of radiated heat then the value of is 273 a 4K then the value of 10a is 18 T Lacee T 273 C T T 0 C 0 0 ice water

Full Marks Zero Marks 0 In all other cases Two conducting rods are joined at P and end A and end B are kept at fixed temperature Temperature variation from A to B is given below k k2 conductivity of rods Find ratio of thermal conductivities of the rods A k P k B Temp 60 30

Steam at 100 C is passed into 1 1 kg of water contained in calorimeter of water equivalent 0 02 kg at 15 C till the temperature of the calorimeter nses to 80 C The mass of steam condensed in kilogram is 0 13 0 065 0260 0135

Apendulum clock keeps correct time at 0 C The thermal coefficient of linear expansion of the material of the pendulum is a If the temperature rises to t C then the clock loses per day by at

In a composite rod when two rods of different lengths and 2 and of the same cross sectional area are joined from end to end then if K is the effective coefficient of thermal conductivity the value of K is AS

Three rods of same dimensions are arranged as shown in the figure They have thermal conductivities K K and K3 The points P and Q are maintained at different temperature For the heat to flow at the same rate along PRQ and PQ Then P 2 K R K K3 1 1 K3 K K 2 K K K K K2 V Q 20 V

A 120 g aluminum cylinder is removed from a liquid nitrogen bath where it has been cooled to 196 C The cylinder is immediately placed in an insulated cup containing 70 0 g of water at 14 0 C Part A What is the equilibrium temperature of this system The average specific heat of aluminum over this temperature range is 65 J kg K Express your answer using one significant figure

A wall has two layers A and B made of different materials The thickness of both the layers is the same The thermal conductivity of A and B are KA and KB such that KA 3KB The temperature across the wall is 20 C In thermal equilibrium MP PET 1996 99 BHU 1997 CPMT 1998 DPMT 2000 RPMT 2005 Kerala PET 2012 The temperature difference across A 15 C The temperature difference across A 5 C The temperature difference across A is 10 C The rate of transfer of heat through A is more than that through B

For cooking the food which of the following type of utensil is most suitable SCRA 1998 MP PMT PET 1998 2000 RPET 2001 High specific heat and low conductivity High specific heat and high conductivity Low specific heat and low conductivity Low specific heat and high conductivity

A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio 1 4 If the free face of brass is at 100 c and that of copper at o c the temperature of interface is CPMT 1996 DPMT 1997 2003 EAMCET 2000 MP PMT 2001 BVP 2004 KCET 2007 80 C 20 C 60 C 40 C

The two ends of a rod of length L and a uniform cross sectional area A are kept at two temperature T and T T T The rate of heat transfer d through the rod in a steady state is given by dt CBSE PMT 2009 dQ kL T T dt dQ k T T LA dt dQ kLA T T dt dQ kA T T 11

ater in a lake starts freezing at t 0 when the outside temperature is 0 C The time intervals in which thickness changes from 0 to y from to 2y from 2y to 3y and so on will be in ratio

A black body emits maximum radiation near a wavelength Am The emissivity of the material is 0 7 If the absolute temperature of the black body is doubled then A The total emitted energy increases 8 times C The maximum radiation occurs at 22m B The total emitted energy increases 16 times D 1 The maximum radiation occurs at

Water of mass 100g at a temperature of 100 C is converted into steam at 100 C The specific latent heat of vaporisation of water is 2300 J g How much thermal energy is absorbed by the water A 23 J B 230 J C 230000 J D 23 000 000 J

Calculate the all possible View factor of cylinder body assume top and bottom surface as 1 and 2 and inside cylinder is 3rd body Take diameter D and length L and the write the all radiation resistance equation Assume the suitable data

Two black spheres P and Q have radii in the ratio 3 2 The wavelengths of maximum intensity radiation are in the ratio 3 4 respectively The ratio of radiated power by P to Q is A B C 74 9 64 9 16 9

TYPE questions Each question has 4 choices 1 Read More How much heat must be supplied to convert 1 kg ice at 10 C to steam at 100 C Take specific heat of ice S 0 5 cal gm C Latent heat of fusion of ice 80 cal gm and Latent heat of vaporization 540 cal gm O 725 kcal 820 kcal 830 kcal 735 kcal

When a hot object is placed in a water bath whose temperature is 25 C it cools from 100 C to 50 C in 160s In another bath the same cooling occurs in 140s Find the temperature of the second bath The temperature of the second bath 1 C

A perfectly conducting pan at 0 C is put on a gas stove at t 0 Stove supplies a constant power P Let be the temperature of the pan at any general time then assuming Newton s law of cooling to hold good The value of will keep on decreasing with time The graph between de and The graph of between de and will be a straight line After sufficiently long time the value of de will approach zero dt will be straight line with negative slope

A closed bottle containing water is opened the moon What will happen A The water will freeze B The water will boil C The water will remain as before stor will decompose into H and 0

4 1 1 Two spheres A and B have the same radii but the heat capacity of A is greater than that of B The surfaces of both are painted black They are heated to the same temperature and allowed to cool in vacuum Then Question Type Single Correct Type A cools faster than B 3 English 2 both A and B cool at the same rate Review Q 4 B cools faster than A at any temperature the ratio of their rates of cooling is a constant

To sterilize a 49 0 g glass baby bottle we must raise its temperature from 21 0 C to 87 0 C How much heat transfer in J is required

On a hypothetical scale X the ice point is 40 and the steam point is 120 For another scale Y the ice point and steam points are 30 and 130 respectively If X reads 50 the reading of Y is A 5 B 8 C 10

500 g of water and 100 g of ice at 0 C are in a calorimeter whose water equivalent is 40 g 10 g of steam at 100 C is added to it Then water in the calorimeter is Latent heat of ice 80 cal g Latent heat of steam 540 cal g 1 580 g 2013 3 600 g 2 590 g 4 610 g

1 4 4 2 10 gm of ice at 5 C is added to 10 gm of water 45 at 60 C Specific heat of water 1 cal gm C specific heat of ice 0 5 cal gm C and latent heat of ice 80 cal gm The resulting temperature of the mixture is 1 0 C 2 2 C 3 2 C 4 10 C 1 7 2 5 C 10 gm 60 C 10 gm fanfare 3 1 cal gm C 4 2 fafere 30 5 cal gm C 31 80 cal gm fer front and 1 0 C 2 2 C 3 2 C 4 10 C

ALLEN An ideal heat engine exhausting heat at 77 C 8 is to have a 30 efficiency It must take heat at 1 127 C 3 327 C 2 227 C 4 673 C var i fer 30 et enfer 1 127 C 3 327 C 2 227 C 4 673 C ander