# Heat Workseets

**Heat** are transferred from one point to another by different methods like **radiation ,convection and conduction**.Here under are the list of the objective questions based on the **transfer of heat**.Answers are at the end of the *worksheets*.Check your ability.

1>In metallic rods the heat flow lakes place by means of

(1) Conduction

(2) Convection

(3) Radiation

(4) Evaporation

2>In which process medium is not required

(1) Conduction

(2) Convection

**(**3) Radiation

(4) All of above processes

3>The speed of heat radiation in vacuum is

(1) Equal to speed of light

(2) Less than the speed of light

(3)Greater than the speed of light

(4) Equal to the speed of sound

4>In steady slate the temperature of a rod

(1) Decreases with time

(2) Increases with time

(3) Does not change with time and is same at every point of rod.

(4) Does not change with time but is different at different points of the rod

5>Heat produced by friction is transferred by

(1) Conduction

(2) Convection

(3) Radiation

(4) All of Above

6>The phenomenon of land and sea breeze is as a result of

(1) Conduction

(2) Convection

(3) Radiation

(4) Evaporation

7>The most appropriate material for a cooking pot processes following characteristics

(1) High specific heat and low conductivity

(2) High specific heat and high conductivity

(3) Low specific heat and low conductivity

(4) Low specific heat and high conductivity

8>The high conductivity of metals is due to

(1) Free electron

(2) Bound electrons

(3) Very close colliding atoms

(4) Free atoms

9>Heat is transmitted from higher -to lower temperature through actual mass motion of the molecules in

(1) Conduction

(2) Convection

(3) Radiation

(4) All of above

10>The amount of heat flowing per unit cross-sectional area of a metallic rod per unit time having unit temperature gradient in steady state is called

(1) Thermal conductivity

(2) Thermal resistance

(3) Convection coefficient

(4) Radiation coefficient

11>Arrange copper, iron and silver in increasing order of thermal conductivity

(1) Iron, silver, copper

(2) Silver, copper, iron

(3) Iron, copper, silver

(4) Copper, iron, silver

12>A metallic rod is continuously heated keeping one end in a hot furnace. The amount of heat flowing in the steady state does not depend upon

(1) Cross-sectional area of the rod

(2) Length of the rod

(3) The temperature gradient

(4) The mass of the rod

13>The rate of flow of heat in a rod in steady state is given by

The thermal conductivity of rod (K) depends on

(1) Cross-sectional area

(2) Rate of flow of heat

(3) Temperature gradient

(4) Material of rod

14>A metallic rod is heated by keeping its one end in a furnace. The steady state is reached. Now the temperature gradient

(1) Is same at all points along the rod

(2) ls greater near the end having the lower temperature

(3) Is greater near the hot end

(4) Increases as we move from hot end to cold end

15>Temperature gradient is

(1) A scalar quantity

(2) A vector quantity

(3) Neither a scalar nor a vector quantity.

(4) Dimensionless

16>The direction of temperature gradient

(1) Is from hotter end to colder end

(2) Is from colder end to hotter end

(3) Is from axis towards surface

(4) Is from surface towards axis

17>The unit of temperature gradient is

(1) ^{o}C-m

(2) m(^{o}C)^{-1}

(3) (^{o}C)m^{-1}

(4) (^{o}C)m^{-2}

18>The unit of thermal conductivity is

(1) Kilocal m(^{o}C)^{-1} sec^{-1}

(2) Kilocal m^{-1}(^{o}C)^{-1} sec^{-1}

(3) (^{o}C)^{-1} sec^{-1} m^{-1} /kilocal

(4) Kilocal sec (^{o}C)^{-1} m^{-1}

19>A metal bar of length “l” is well lagged with some non-conducting material to prevent losses of heat from its surface and the two ends are then maintained at steady temperatures and with , then in steady state, the temperature of a section of a bar at a distance x from the hot end varies as shown in graph

20>A man would feel iron and wooden blocks equally cold or hot at

(1) 98.6°C

(2) 98.6°F

(3) 98.6 K

(4) No temperature

21>Woolen clothes keep the body warm because

(1) Wool increases the temperature of the body

(2) Wool absorbs radiant heat from atmosphere**.**

(3) Wool is a bad conductor of heat, so it will not allow heat to flow out from the body

(4) Heat radiated from the body experience repulsive force by the wool and returns back

22>The radiation emitted by a perfectly black body is proportional to

(1) Temperature on ideal gas scale

(2) Square of temperature on ideai gas scale

(3) Fourth power of temperature on ideal gas scale

(4) Fourth power of temperature on Celsius scale

23>Newton’s law of cooling is used in laboratory to find

(1) Specific heat of gases

(2) Specific heat of liquids

(3) Latent heat of liquids

(4) Density of liquids

24>Hot water is poured in a glass-tumbler. If it cracks, it is due to following property of glass

(1) Low thermal conductivity

(2) High thermal conductivity

(3) High specific heat

(4) High melting point

25>A metal piece is heated up to absolute temperature T. The temperature of surroundings is t^{o }absolute. The net heat lost by the piece to the surroundings is proportional to

(1) ( T – t )^{4}

(2) T^{4}

(3) T^{2} – t^{2}

(4) T^{4} – t^{4}

26> According to Wein’s law

(1) T = constant

(2) = constant

(3) = constant

(4) = constant

27>It is hotter for the same distance over the top of the fire than it is up the side of it mainly because

(1) Air conducts heat upward

(2) Heat is radiated upward

(3) Convection takes more heat upward

(4) Conduction, convection and radiation all contribute significantly in transferring heat upwards

28>Water in a beaker is heated to a temperature and surrounding temperature is then ,Newton’s law of cooling [ i.e will hold if

(1)

(2)

(3)

(4)

29>Kirchoff’s law of radiation states that

(1) Good emitters are good absorbers

(2) Good reflectors are good emitters

(3) Good emitters are bad absorber**s**

(4) White surfaces are good emitters

30>The absorptive power of a black body is

(1) 100%

(2) 50%

(3) Zero%

(4) Infinity

31>The relative emissive power of a black body is

(1) 0

(2) 0.5

(3) 1.0

(4) Infinity

32>In arbitrary units at a given temperature the emissive power of a body is 8 and absorptive power is 0.5. Then the emissive power of black body at that temperature wiil be

(1) 4

(2) 16

(3)

(4) Uncertain

(33)Four identical pieces of copper are painted with different types of paints. Which one would you expect to lose heat most rapidly if they are all heated to the same temperature and allowed to cool in vacuum.

(1) Painted rough black

(2) Painted rough white

(3) Painted shiny white

(4) Painted shiny black

(34)Two persons A and B are of equal cold tolerance. A wears white shirt and B wears black shirt of same thickness. They are wandering in cold weather. Which person is more likely to suffer cold?

(1) A

(2) B

(3) Both A and B

(4) Nothing can be said

35>A block of steel heated to 100°C is left in a room to cool. Which of the curves shown in fig. represents the correct cooling behavior?

36>Two walls of thicknesses d_{1} and d_{2} and thermal conductivities K_{1} and K_{2} are in contact. In

steady state the temperature at the outer surfaces are T_{1} and T_{2}, then the temperature (T)

of the common wall will be

(1)

(2)

(3)

(4)

37> Two metallic plates of equal thickness and thermal conductivities K_{1} and K_{2} are put together face to face and a common plate is constructed, then the equivalent thermal conductivity of the plate will be

(1)

(2)

(3)

(4)

38>Two metallic plates of equal length and thermal conductivities K_{1} and K_{2} are put together such that their ends coincide. If their cross-sectional areas are the same, then the equivalent thermal conductivity of the combination will be

(1)

(2)

(3)

(4)

39>A cylinder of radius R made of a material of thermal conductivity K is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K_{2}. 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

(1)

(2)

(3)

(4)

40>A metallic rod has length l, cross-sectional area A and conductivity K. Then its thermal resistance is

(1)

(2)

(3)

(4) Zero

41>Two identical square rods of metal are welded end to end as shown in fig (a); 50 cal of heat flows in 8 minutes. If the rods are welded as shown in fig (b), the same amount of heat will flow through the rod in

(1) 2 min

(2) 4 min

(3) 3 min

(4) 32 min

42>Two identical vessels are filled with equal amounts of ice. The vessels are made from different materials of thermal conductivities K_{1} and K_{2} respectively. If the times taken by the ice to melt in these vessels are t_{1} and t_{2} respectively; then the ratio of thermal conductivities K_{1} : K_{2} is

(1) t_{2} : t_{1}

(2) t_{1} : t_{2}

(3) t_{2}^{2} : t_{1}^{2}

(4) t_{1}^{2} : t_{2}^{2}

43>A compound slab is composed of two parallel layers of different materials. One layer has thickness 3 cm and coefficient of thermal conductivity kilocal/m°C sec and the other of thickness 2 cm and thermal conductivity 1.6 X 10^{-2} kilocal/m°C sec. If the temperatures of the outer faces, of the composite slab are maintained at 100°C and 0°C, then the temperature of the junction is

(1) 100°C

(2) 60°C

(3) 40°C

(4) 0°C

44>The ends of two rods of different materials with their thermal conductivities, radii of cross- sections and lengths all in the ratio 1 : 2 are maintained at the same temperature difference. If the rate of flow of heat in the larger rod is 4cal/sec, then that in shorter rod in cal/sec will be

(1) 1

(2) 2

(3) 8

(4) 16

45>In a steady state, the temperature of the ends A and B of a 20 cm long rod AB are 100°C and 0°C. The temperature of the point distant 9 cm from A

(1) 45°

(2) 55°

(3) 60°

(4) 65°

46> Two identical long rods made of different materials of thermal conductivities K_{1} and K_{2} are coated with wax and have their one end immersed in hot bath of oil. If the lengths of wax melted in steady state be l_{1} and l_{2}, then

(1)

(2)

(3)

(4)

47>A black body radiates energy at the rate of E

watt/m^{2} at a high temperature T K. When the temperature is reduced to T/2 K, the radiant

energy will be

(1)

(2) 4 E

(3)

(4) 16 E

48>A black body is at a temperature of 500 K. It emits energy at the rate which is proportional to

(1) 500

(2) ( 500 )^{2}

(3) ( 500 )^{3}

(4) ( 500 )^{4}

49>A black body is at a temperature 727° .It

emits energy at the rate which is proportional to

(1) 727

(2) (727)^{4}

(3) 1000

(4) (1000)^{4}

50>The rate of radiation of a black body at 0°C is E joule/sec. The rate of radiation of the black body at 273°C will be

(1) E

(2) 4 E

(3) 8 E

(4) 16 E

51>If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor of

(1) 2

(2) 4

(3) 8

(4) 16

52>In Wien’s displacement law = b. The value of b is nearly equal to

(1) 0.3 cm K

(2) 3 cm K

(3) 30 cm K

(4) cm K

53>The temperature of a furnace is 2327°C and the intensity of maximum in its radiation spectrum is nearly at 12000 A. If the intensity in the spectrum of a star is maximum nearly at 4800 A, then the surface temperature of the star is

(1) 767°C

(2) 1040°C

(3) 6500°C

(4) 6227°C

54>Two stars A and B radiate maximum energy at 3600A and 4800 A respectively . Then the ratio of absolute temperature of A and B is

(1) 4 : 3

(2) 3 : 4

(3) 256 : 81

(4) 81 : 256

55>Solar radiation emitted by the sun resembles that emitted by a black body at a temperature of 6000 K. Maximum intensity is emitted at a wavelength of about 4800 A. If the sun were

to cool down from 6000 K to 3000 K, then the peak intensity would occur at a wavelength

(1) 2400 A

(2) 4300 A

(3) 9600 A

(4) 19200 A

56>In an atom bomb, a temperature of about 10 million degrees is developed at the moment of explosion. In what region of the spectrum do the wavelength corresponding to maximum energy density lie if the light source is in the atom bomb

(1) Ultraviolet region

(2) Visible region

(3) Infrared region

(4) X-ray region.

57>The original temperature of a black body is 727^{o }C. The temperature to which this black

body must be raised so as to double the total radiant energy is

(1)917 K

(2) 1190 K

(3) 1454°C

(4) 2000 K

58>Two solid spheres of radii R_{1} and R_{2}; are heated to the same temperature and allowed to cool under similar conditions. Their rates of cooling are in the ratio of

(1)

(2)

(3)

(4)

59>Two solid spheres of radii R_{1} and R_{2} are heated to same temperature and allowed to cool under similar conditions. Their loss of heat are in the ratio

(1)

(2)

(3)

(4)

60>Two spheres of the same material have radii 1m and 4 m and temperature 4000K and 2000K respectively. The energy radiated per second by the first sphere is

(1) Greater than that by the second.

(2) Less than that by the second.

(3) Equal in both cases.

(4) The information is incomplete to draw any conclusion

61>A bucket full of water is kept in a room and it cools from 70°C to 65°C in t_{1 }min and from 65°C to 60°C in t_{2 }min and from 60°C to 50°C in t_{3} min then

(1) t_{1} < t_{2} < t_{3}

(2) t_{1} > t_{2} > t_{3}

(3) ) t_{1} = t_{2} = t_{3}

(4) ) t_{1}, t_{2}, t_{3 }can not be compared

62> Hot water kept in a beaker placed in a room cools from 60°C to 50°C in 5 minutes . The time taken by it to cool from 50°C to 40°C is

(1) 5 min

(2) Less than 5 min

(3) More than 5 min

(4) Depends on quantity of water in the beaker

63>Certain substances emit only the wavelengths when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths

(1)

(2)

(3)

(4)

64> A black body at a certain temperature T K emits radiation proportional to T^{4}.If another body is at same -temperature T but having relative emissivity 0.4, will emit radiation proportional to

(1) T^{2}

(2) T^{4}

(3) T^{1.6}

(4) T^{10}

65>Equal temperature difference exists between the ends of two metallic rods 1 and 2 of equal lengths. Their thermal conductivities are K_{1} and K_{2} and cross-sectional areas A_{1} and A_{2}.The condition for equal rate of heat transfer will be

(1)

(2)

(3)

(4)

66>At a specific temperature, the energy densities for a black body for three different wavelengths are 10, 19 and 7 units. For these wavelengths if the absorption coefficient of a body is respectively 0.8 , 0.3 and 0.9, then the emissive powers of this body for these wavelengths are in the ratio

(1) 10 : 19 : 7

(2) 8 : 3 : 9

(3) 8 : 5.7 : 6.3

(4) 8 : 9.5 : 4.3

67>The ends of rods of lengths l and radius r of the same material are kept at the same temperatures. Which of the rod conducts most heat ?

(1) l = 1 m , r = 1 cm

(2) l = 2 m , r = 1 cm

(3) l = 2 m , r = 2 cm

(4) l = 1 m , r = 2 cm

68>The coefficients of thermal conductivity of copper, mercury and glass are respectively K_{c},

K_{m} and K_{g} such that K_{c} > K_{m} > Kg. If the same quantity of heat is to flow per second per

unit area of each and corresponding temperature gradients are X_{c}, X_{m} and X_{g}, then

(1) X_{c} = X_{m} = X_{g}

(2) X_{c} > X_{m} > X_{g}

(3) X_{c} < X_{m} < X_{g}

(4) X_{m,} < X_{c} < X_{g}

69>The spectrum from a black body radiation is

(1) Line spectrum

(2) Band spectrum

(3) Continuous spectrum

(4) Fraunhoffer spectrum

70>The solar constant is

(1) 1400 W/m^{2}

(2) 1.4 W/m^{2}

(3) 2 W/m^{2}

(4) A variable parameter

71>A body cools from 50°C to 49.9°C in 5 seconds. How much time will it take in cooling from 40°C to 399°C (Assume the temp. of surroundings to be 30°C)

(1) 2.0 s

(2) 2.5 s

(3) -10 s

(4) 20 s

72>Newton’s law of cooling is a special case of

(1) Stefan’s law

(2) Wein’s law

(3) Kirchoff’s law

(4) Planck’s law

73>Newton’s law of cooling is also applicable to

(1) Natural convection losses

(2) Forced convection losses

(3) Conduction losses

(4) All of above

74>A cube, a sphere, a circular plate made of same material and heated to the same mass are heated to the same high temperature (say 150°C). Which one cools at the slowest rate when put in the same surroundings.

(1)The sphere

(2) The cube

(3) The circular plate

(4)The rate of cooling will be same for all three

75>The coefficient of reflectivity of black body is

(1) 1

(2) 0.5

(3) 0

(4) Infinite

76>A graph plotted between logarithmic of temperature difference between body and surrounding and time is (provided temperature difference is small so that Newton’s law holds)

(1) Straight line

(2) Parabola

(3) Circle

(4) Oblique ellipse

77>A piece of ice placed in a room

(1) Does not radiate

(2) Radiates less but absorbs more

(3) Radiates more but absorbs less

(4) Radiates as much as it receives

78>Energy emitted by a black body and wavelength relations at temperature

T_{1}K , T_{2}K and T_{3}K are shown by curves. The relation be

(1) T_{3 }> T_{2} > T_{1 }

(2) T_{3 }< T_{2} < T_{1}

(3) T_{3 }= T_{2} = T_{1}

(4) T_{1 }, T_{2} , T_{3 }bear no relation

79> The graph represents the energy (E) radiated per unit area per sec against wavelength of radiation. The area under the curve is found to be proportional to

(1) T^{5}

(2) T^{4 }

(3) T^{2 }

(4) T

80>Fig. represents a curve showing the distribution of energy density of a black body at a certain temperature. This curve corresponds to an approximate temperature

(1) 100 K

(2) 2000 K

(3) 200 K

(4) 5000 K

81>A blue glass when heated will glow initially with

(1) Blue color

(2) Yellow color

(3) Red color

(4) White color

82>The color of a star is an indication of its

(1) Size

(2) Distance from earth

(3) Weight

(4) Temperature

83>Out of three stars Red, Blue and Yellow; which one is hottest

(1) Red

(2) Blue

(3) Yellow

(4) All are equally hot

84>Following laws of radiation, cadmium salt when put into a bunsen flame give red color to the flame. If while light from a tungsten, filament lamp is made to pass through a bulb containing cadmium vapors, the transmitted light will be

(1) Red

(2) Blue

(3) White

(4) Green

Evaluate yourself by checking your answers here.

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