Transmission of heat Questions and Answers

You have two rods of the same length and diameter but they are formed for different materials The rods will be used to connect two regions of different temperature such that energy will transfer through the rods by heat They can be connected in series as in part a of the figure below or in parallel as in part b In which case is the rate of energy transfer by heat larger Th Rodl a Rod2 A when the rods are in series C the rate is the same in both cases T Th Rodl Rod2 T b B when the rods are in parallel D cannot be determined

A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t The metallic rod is melted and the material is formed into a rod of half the radius of the original rod What is the amount of heat conducted by the new rod when placed in thermal contact with the two reservoirs in time t 1 2 20 2

25 The two ends of a uniform lagged rod of thermal conductivity k are maintained at different but constant temperatures do The temperature gradient at any point on the rod is equal to the difference in temperature per unit length Th de heat flow per unit time per unit cross section of the rod is I do A is the same for all points on the rod de B I will decrease as we move from higher to lower temperature C I k de de I don options are incorrect

What is the temperature T at the interface if heat conductivity of first slab of length is K and is uniform every where but the conductivity of second slab of length 2 varies with the distance x measured from the interface according to the law K K 1 The temperature at the boundries of the composite slab are 2T and T A T C T 2ln2 1 n2 1 n3 1 20n3 1 T B T T D T 20n3 1 n3 1 4n3 1 en3 1 To T 21 K K K 1 4 21

7 The temperature at the bottom of a pond of depth L is 4 C The temperature of the air just above the layer of ice frozen at the pond s surface is 2 C for the past many days The thermal conductivity of ice is three times that of water The thickness of the frozen layer of ice must be A 2L 3 BYL 2 C L 3 D 3L 5

der of radius R of thermal conductivity K is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of thermal conductivity K The two ends of the whole system are maintained at two different temperatures T and T T T The system is in steady state and there is no loss of heat across cylinderical surface The electrical thermal conductivity of the system is CG PMT 2015 KCET 2013 2R c K G T a K K K K 3K 4 T Cylinder of radius R b K d K K K K K 3K K 4

A 100 watt electric heating element is placed in a pan containing one litre of water Although the heating element is on for a long time the water though close to boiling does not boil When the heating element is removed approximately how long will it take the water to cool by 1 C Assume that the specific heat for water is 4 2 kilojoules kilogram C A 20 s B 42 s C 60 s D 130 s

5 A vertical wooden cylinder AB of uniform cross section and closed at both ends and of length 1 10 m contains mercury occupying a column of length 10 cm at 0 C Initially the cylinder is vertical with end A below B Without raising the cylinder it is quickly inverted about its centre so that remaining vertical the end B is below A The procedure is repeated to bring A again below B This process is repeated quickly 100 times Assuming that the thermal energy during the process is absorbed by mercury and specific heat of mercury 140 J kg K and coefficient of cubical expansion of mercury is 1 8 x 104 K the increase in the temperature of mercury is Ignore the expansion of the wooden cylinder A 21 C B 14 C nerv C 15 4 C D 25 2 C

section are maintained at temperature T and T2 T T as shown in the figure 1 X T If I is heat current through the cross section of conductor at distance x from its left face then the variation of with x is best represented by 3 t 2 T 4 Drs

cylinder of mass 0 5 kg is heated electrically by a 12 W heater in a room at 15 C Th cylinder temperature rises uniformly to 25 C in 5 min and finally becomes constant at 45 Assuming that the rate of heat loss is proportional to the excess temperature over surroundings A the rate of loss of heat of the cylinder to surrounding at 20 C is 2 W B the rate of loss of heat of the cylinder to surrounding at 45 C is 12 W 240 C specific heat capacity of metal is J kg C In 3 2 D none of the above

Find the temperature of junction shown in figure for three rods identical in dimensions 80 C 2 K K 3 K 20 C

A fan with copper winding in its motor consumes less power as compared to an otherwise similar fan having aluminium winding Explain 9 The thermal

D Write True or False for the following 1 A clinical thermometer can be used to measure temperature of ice 2 A laboratory thermometer has a range from 10 to 110 C 3 Sea breeze occurs as a result of conduction 4 All gases including air are bad conductors of heat 5 All hot bodies radiate heat energy 6 The sun s heat reaches us by conduction convection and radiation

4 Four spheres A B C and D of different metals but of same radius are kept at same temperature The ratio of their densities is 2 3 5 1 If specific heats of their materials are in the ratio 3 6 2 4 which sphere will show initially the fastest rate of cooling a D b C c B d A

D and E of 3 A composite block is made of slabs A B different thermal conductivities given in terms of a constant K and sizes given in terms of length L as shown in the figure All slabs are of same width Heat Q flows only from left to right through the blocks Then in steady state heat 1L 3L 4L 0 A 2K 1L B 3K C 4K D 5K 5L 6L E 6K a heat flow through A and E slabs are same b heat flow through slab E is maximum c temperature difference across slab E is smallest d heat flow through C heat flow through B heat flow th

1 A steel ball of mass m 1 kg moving with velocity 50 m s collides with another ball of mass m2 200 gm lying on the ground During the collision their internal energies change equally and T and 7 are the rise in temperatures of masses my and my respectively If specific heat of steel is 0 105 and J 4 18 J cal then a T 7 1 C and T 1 47 C b T 1 47 C and T 7 1 C c T 3 4K and T 17 0K d T 7 1K and T LAV

is the eet sch of black body radiation a c Intensity b Intensity Wavelength d Wavelength atic representation of the graph T T T Wavelength T T Wavelength T T T T T Intensity T T T T T T

A planet having surface temperature T has solar constant S An angle 0 is subtended by the sun at planet then 1 ST2 3 S0 2 ST 1 S 0

Two identical rods are connected in series a 100 joule heat is transferred in 10 seconds F the time taken to transfer same amount of hea the rods are connected in parallel keeping temperature of ends same as before 1 1 25 s 2 2 5 s

21 Three identical thermal conductors are connected as shown in figure Consider no heat lost due to radiation the temperature of the junction is 1 60 C 3 50 C 20 C 60 C 2 20 C 4 10 C 70 C

5 Standard free energies of formation in kJ mol at 298 K are 237 2 394 4 and 8 2 for H O 1 CO g and pentane g respectively The value of Ecell for the pentane oxygen fuel cell is

100 g ice at 0 C is mixed with 10 g steam 100 C then mixture has 1 20 g ice and 90 g water 2 10 g ice and 100 g water 3 80 g ice and 30 g water 4 10 g ice and 40 g water

The graph between radiation power from a linear antenna and square of length of antenna is given in the figure for two antenna A and B If all oth parameter are same then find ratio of wavelength of A and B P W

1 4 cm 2 40 cm 3 44 cm 4 440 cm Rate of heat flow through two conducting rods of identical dimensions having thermal conductivities K and K are Q and Q when their ends are maintained at the same difference of temperature individually When the two rods are joined in series with their ends maintained at the same temperature difference as shown in the figure the rate of heat flow will be 0 0 0 1 3 0 K K Q Q 2 K Q K Q K K 0 2 K Q K Q Q Q

loss if the number of grey bags sold is 5400 The temperature at 12 noon was 10 C above zero If it decreases at the rate of 2 C p hour until midnight at what time would the temperature be 8 C below zero What wou be the temperature at midnight

A sphere and cube of same material and same volume are heated upto the same temperature and allowed to cool in the same surrounding The ratio of the amount of radiations emitted will be 1 1 1 3 EC 1 3 1 4t 2 3 4 1 4t 2 3 1 28 A ba to in

Aakash Rank Booster Test Series for Two ends of a uniform conductor of length are at temperature differences 100 C The temperature from one end is about 1 at point P at distance 4 Assuming heat transfers by conduction only 1 4 0 C 1 25 C 2 66 7 C P 100 C 2 33 3 C 4 100 C

The coefficient of emission for perfectly black body is azero binfinity efone dless than one

of curved surface of rods is completely insulated the rate of heat flow through AB is H The rate of heat flow through BD is 100 C 0 C 2H 3 H E B D FIGURE 11 47 b H 3 100 R d none of these x 31 41 28 3 2 100x3 87

1 HRT in 2 2 MRT In 2 nRT In 2 3 4 2nRT In 41 In a cold storage ice melts at the rate of 2 Kg h when the external temperature is 20 C Find the minimum power output of the motor used to drive the refrigerator which just prevents the ice from melting Latent heat of fusion of ice 80 calig 1 28 5 W 2 40 5 W 4 13 6 W 3 30 W mi slightly displaced vertically from the equilibrium position fuortical oscillations The

Four spheres A B C and D have their radii in arithmetic progression and the specific heat capacities of their substances are geometric progression If the ratios of heat capacities of D and B to that of C and A are as 8 27 The ratio of masses of B and A is assume same density for all spheres a 8 1 c 1 8 b 4 1 d 1 4

44 Instantaneous temperature difference between cooling body and the surroundings obeying Newton s law of cooling is 0 Which of the following represents the variation of In 0 with time t 1 22 0 0 even begn In 0 3 In e 0 0 NO t 2 4 In e 0 0 In e b 0 0 t

Four identical metal rods are connected as shown in figure Assume there is no heat loss through side walls of the rods and no radiation loss the junction temperature in steady state is 1 22 C oror 20 C 10 C 30 C 40 C 2 26 C ZAX 3090

Find the rate of heat flow through a cross section of the rod shown in figure T T Thermal conductivity of he material of the rod is K Dir

A body cool from 90 C to 70 C in 10 minutes if temperature of surrounding is 20 C find the time taken by body to cool from 60 C to 30 C Assuming Newton s law of cooling is valid 1 10 min 2 24 min 3 36 min 4 8 min

1 Three objects coloured black gray and white ca withstand hostile conditions upto 2800 C Thes objects are thrown into a furnace where each c them attains a temperature of 2000 C Which object will gloss brightest 1 The white object 2 The black object 3 All glow with equal brightness 4 Gray object

Two metal cubes with 3 cm edges of copper and aluminium are arranged as shown in figure Find Al Cu b 100 C 20 C D The total thermal current from one reservoir to the other The ratio of the thermal current carried by the copper cube to that carried by the aluminium cul Thermal conductivity of copper is 60 W m K and that of aluminium is 40 W m K

24 A perfectly black body radiates 25 joule sec at 600 K The temperature at which an ordinary body of same area and emissivity 0 0256 would have same rate of emission is b 1000 K a 1200 K c 900 K d 1500 K 5 Two concentric perfectly black spheres are maintained at temperatures 200 K and 300 K respectively If the net rate of energy transfer per unit area between two spheres is 56x10watt im K

A solid sphere solid cylinder and circular disc o same material and mass are maintained at same temperature The body which is cooling at fastest rate is 1 Solid sphere 3 Circular disc 2 Solid cylinder 4 All same

Heat is incident on a athermanous body having emissivity 0 8 at the rate of 10 watt The quantity of heat reflected by it in two minutes is c 480 J d 240 J a 120J b 960J diote

Suppose you stand with one foot on ceramic flooring and one foot on a wool carpet making contact over an area of 75 0cm with each foot Both the ceramic and the carpet are 5 00 cm thick and are 12 0 C on their bottom sides At what rate must heat transfer occurs from each foot to keep the top of the ceramic and carpet at 38 0 C Pcarpet Blank 1 Pceramic Blank 2 Round your answers to the nearest 2 decimal places Blank 1 Add your answer

Your 21 C bedroom uses a spherical bulb operating at a temperature of 2093 C Assuming that the diameter of the bulb is 19 56 cm and its emissivity is 0 88 find the rate of heat flow Round your answer to 0 decimal places

Question 4 10 Points Your 27 C bedroom uses a spherical bulb operating at a temperature of 2027 C Assuming that the diameter of the bulb is 18 39 cm and its emissivity is 0 81 find the rate of heat flow Round your answer to 0 decimal places Add your answer

Question 5 10 Points A steel iron metal rod is joined end to end with a stainless steel rod It is known that the two metals have the same radius r 0 45 cm the length of steel iron is 6 01 m and the length of stainless steel is 7 27 m If the free end of steel iron is subjected to 224 C while the free end of stainless steel is subjected to 12 C find the temperature at the junction Round your answer to 2 decimal places Add your answer

A steel iron metal rod is joined end to end with a stainless steel rod It is known that the two metals have the same radius r 0 36 cm the length of steel iron is 2 96 m and the length of stainless steel is 8 83 m If the free end of steel iron is subjected to 166 C while the free end of stainless steel is subjected to 62 C find the temperature at the junction Round your answer to 2 decimal places

A steel bar 12 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 team 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 keu 385 W m K Round your answer to 2 decimal places

At what net rate does heat radiate from a 273 m black roof on a night when the roof s temperature is 14 83 C and the surrounding temperature is 33 89 C The emissivity of the roof is 0 849 Round your answer to 0 decimal places

A scientist is trying to determine the specific heat of 10 0 g of an unknown substance He heats up the substance to a temperature of 100 0 C and places it in 1 02 kg of water at 22 0 C He notices that the final temperature of the water and substance is 23 1 C What is the specific heat of the substance in J kg C 1 Point O5210 O8320 O 4020

Energy transferred as heat always moves from an object at higher temperature to an object at lower temperature an object with higher mass to an object with lower mass an object with lower mass to an object with higher mass O an object in a higher location to an object in a lower location an object at lower temperature to an object at higher temperature an object with low kinetic energy to an object with high kinetic energy

How much heat is required to melt 5 5 kg of ice at 9 C