JEE Main & Advanced Physics Transmission of Heat Question Bank

done Conduction Total Questions - 68

• question_answer1)
  In which case the thermal conductivity increases from left to right                            [NCERT 1974, 76; AFMC 2000]
  A)
             Al, Cu, Ag                               done clear
  B)
             Ag, Cu, Al done clear
  C)
             Cu, Ag, Al                               done clear
  D)
             Al, Ag, Cu done clear
  View Solution play_arrow

• question_answer2)
  Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature [CPMT 1981; NCERT 1973, 81; MP PMT 1987; CBSE PMT 1995]
  A)
             Length 1 m; radius 1 cm done clear
  B)
             Length 2 m; radius 1 cm done clear
  C)
             Length 2 m; radius 2 cm done clear
  D)
             Length 1 m; radius 2 cm done clear
  View Solution play_arrow

• question_answer3)
  The heat is flowing through two cylindrical rods of same material. The diameters of the rods are in the ratio 1 : 2 and their lengths are in the ratio 2 : 1. If the temperature difference between their ends is the same, the ratio of rate of flow of heat through them will be [NCERT 1982; CBSE PMT 1995; EAMCET 1997]
  A)
             1 : 1                                           done clear
  B)
             2 : 1 done clear
  C)
             1 : 4                                           done clear
  D)
             1 : 8 done clear
  View Solution play_arrow

• question_answer4)
  Two identical square rods of metal are welded end to end as shown in figure (i), 20 calories of heat flows through it in 4 minutes. If the rods are welded as shown in figure (ii), the same amount of heat will flow through the rods in                    [NCERT 1982]
  A)
             1 minute                                 done clear
  B)
             2 minutes done clear
  C)
             4 minutes                               done clear
  D)
             16 minutes done clear
  View Solution play_arrow

• question_answer5)
  For cooking the food, which of the following type of utensil is most suitable [MNR 1986; MP PET 1990; CPMT 1991; SCRA 1998; MP PMT/PET 1998, 2000; RPET 2001]
  A)
             High specific heat and low conductivity done clear
  B)
             High specific heat and high conductivity done clear
  C)
             Low specific heat and low conductivity done clear
  D)
             Low specific heat and high conductivity done clear
  View Solution play_arrow

• question_answer6)
  Under steady state, the temperature of a body [CPMT 1978]
  A)
             Increases with time done clear
  B)
             Decreases with time done clear
  C)
             Does not change with time and is same at all the points of the body done clear
  D)
             Does not change with time but is different at different points of the body done clear
  View Solution play_arrow

• question_answer7)
  The coefficient of thermal conductivity depends upon  [MP PET/PMT 1984; AFMC 1996; Orissa JEE 2005]
  A)
             Temperature difference of two surfaces done clear
  B)
             Area of the plate done clear
  C)
             Thickness of the plate done clear
  D)
             Material of the plate done clear
  View Solution play_arrow

• question_answer8)
  When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time every point of the rod attains a constant temperature, then [MP PET/PMT 1988]
  A)
             Conduction of heat at different points of the rod stops because the temperature is not increasing done clear
  B)
             Rod is bad conductor of heat done clear
  C)
             Heat is being radiated from each point of the rod done clear
  D)
             Each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat done clear
  View Solution play_arrow

• question_answer9)
  The length of the two rods made up of the same metal and having the same area of cross-section are 0.6 m and 0.8 m respectively. The temperature between the ends of first rod is \[{{90}^{o}}C\] and \[{{60}^{o}}C\]and that for the other rod is 150 and \[{{110}^{o}}C\]. For which rod the rate of conduction will be greater
  A)
             First                                          done clear
  B)
             Second done clear
  C)
             Same for both                      done clear
  D)
             None of the above done clear
  View Solution play_arrow

• question_answer10)
  The ratio of thermal conductivity of two rods of different material is 5 : 4. The two rods of same area of cross-section and same thermal resistance will have the lengths in the ratio                    [MP PET 1984; BVP 2003]
  A)
             4 : 5                                           done clear
  B)
             9 : 1 done clear
  C)
             1 : 9                                           done clear
  D)
             5 : 4 done clear
  View Solution play_arrow

• question_answer11)
  The thermal conductivity of a material in CGS system is 0.4. In steady state, the rate of flow of heat 10 cal/sec-cm2, then the thermal gradient will be                                                             [MP PMT 1989]
  A)
             \[10{}^\circ C/cm\]             done clear
  B)
             \[12{}^\circ C/cm\] done clear
  C)
             \[25{}^\circ C/cm\]             done clear
  D)
             \[20{}^\circ C/cm\] done clear
  View Solution play_arrow

• question_answer12)
  Two rectangular blocks A and B of different metals have same length and same area of cross-section. They are kept in such a way that their cross-sectional area touch each other. The temperature at one end of A is 100°C and that of B at the other end is 0°C. If the ratio of their thermal conductivity is 1 : 3, then under steady state, the temperature of the junction in contact will be           [MP PMT 1985]
  A)
             25°C                                          done clear
  B)
             50°C done clear
  C)
             75°C                                          done clear
  D)
                  100°C done clear
  View Solution play_arrow

• question_answer13)
  Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 30 minutes. The ratio of their thermal conductivities will be     [MP PMT 1989; CMEET Bihar 1995]
  A)
             1.5  done clear
  B)
             1 done clear
  C)
             2/3 done clear
  D)
             4 done clear
  View Solution play_arrow

• question_answer14)
  Two rods A and B are of equal lengths. Their ends are kept between the same temperature and their area of cross-sections are \[{{A}_{1}}\]and \[{{A}_{2}}\]and thermal conductivities \[{{K}_{1}}\] and \[{{K}_{2}}\]. The rate of heat transmission in the two rods will be equal, if [MP PMT 1991; CBSE PMT 2002]
  A)
             \[{{K}_{1}}{{A}_{2}}={{K}_{2}}{{A}_{1}}\]                     done clear
  B)
             \[{{K}_{1}}{{A}_{1}}={{K}_{2}}{{A}_{2}}\] done clear
  C)
             \[{{K}_{1}}={{K}_{2}}\]      done clear
  D)
             \[{{K}_{1}}A_{1}^{2}={{K}_{2}}A_{2}^{2}\] done clear
  View Solution play_arrow

• question_answer15)
  In variable state, the rate of flow of heat is controlled by
  A)
             Density of material             done clear
  B)
             Specific heat done clear
  C)
             Thermal conductivity         done clear
  D)
             All the above factors done clear
  View Solution play_arrow

• question_answer16)
  If the ratio of coefficient of thermal conductivity of silver and copper is 10 : 9, then the ratio of the lengths upto which wax will melt in Ingen Hausz experiment will be [DPMT 2001]
  A)
             6 : 10                                         done clear
  B)
             \[\sqrt{10}:3\] done clear
  C)
             100 : 81                                    done clear
  D)
             81 : 100 done clear
  View Solution play_arrow

• question_answer17)
  The thickness of a metallic plate is 0.4 cm. The temperature between its two surfaces is \[{{20}^{o}}C\]. The quantity of heat flowing per second is 50 calories from \[5c{{m}^{2}}\] area. In CGS system, the coefficient of thermal conductivity will be
  A)
             0.4  done clear
  B)
             0.6 done clear
  C)
             0.2  done clear
  D)
             0.5 done clear
  View Solution play_arrow

• question_answer18)
  In Searle's method for finding conductivity of metals, the temperature gradient along the bar    [MP PMT 1984]
  A)
             Is greater nearer the hot end done clear
  B)
             Is greater nearer to the cold end done clear
  C)
             Is the same at all points along the bar done clear
  D)
             Increases as we go from hot end to cold end done clear
  View Solution play_arrow

• question_answer19)
  The dimensions of thermal resistance are
  A)
             \[{{M}^{-1}}{{L}^{-2}}{{T}^{3}}K\]                                    done clear
  B)
             \[M{{L}^{2}}{{T}^{-2}}{{K}^{-1}}\] done clear
  C)
             \[M{{L}^{2}}{{T}^{-3}}K\] done clear
  D)
             \[M{{L}^{2}}{{T}^{-2}}{{K}^{-2}}\] done clear
  View Solution play_arrow

• question_answer20)
  A piece of glass is heated to a high temperature and then allowed to cool. If it cracks, a probable reason for this is the following property of glass                                        [CPMT 1985]
  A)
             Low thermal conductivity done clear
  B)
             High thermal conductivity done clear
  C)
             High specific heat done clear
  D)
             High melting point done clear
  View Solution play_arrow

• question_answer21)
  Two walls of thicknesses d1 and d2 and thermal conductivities k1 and k­2 are in contact. In the steady state, if the temperatures at the outer surfaces are \[{{T}_{1}}\] and \[{{T}_{2}}\], the temperature at the common wall is [MP PMT 1990; CBSE PMT 1999]
  A)
             \[\frac{{{k}_{1}}{{T}_{1}}{{d}_{2}}+{{k}_{2}}{{T}_{2}}{{d}_{1}}}{{{k}_{1}}{{d}_{2}}+{{k}_{2}}{{d}_{1}}}\]         done clear
  B)
             \[\frac{{{k}_{1}}{{T}_{1}}+{{k}_{2}}{{d}_{2}}}{{{d}_{1}}+{{d}_{2}}}\] done clear
  C)
             \[\left( \frac{{{k}_{1}}{{d}_{1}}+{{k}_{2}}{{d}_{2}}}{{{T}_{1}}+{{T}_{2}}} \right){{T}_{1}}{{T}_{2}}\]   done clear
  D)
             \[\frac{{{k}_{1}}{{d}_{1}}{{T}_{1}}+{{k}_{2}}{{d}_{2}}{{T}_{2}}}{{{k}_{1}}{{d}_{1}}+{{k}_{2}}{{d}_{2}}}\] done clear
  View Solution play_arrow

• question_answer22)
  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 \[{{35}^{o}}C\] and that of copper at \[1:\sqrt{2.5}\], the temperature of interface is [IIT 1981; MP PMT 1987, 2001]
  A)
             80°C                                          done clear
  B)
             20°C done clear
  C)
             60°C                                          done clear
  D)
             40°C done clear
  View Solution play_arrow

• question_answer23)
  The temperature gradient in a rod of 0.5 m long is \[{{80}^{o}}C/m\]. If the temperature of hotter end of the rod is\[{{30}^{o}}C\], then the temperature of the cooler end is
  A)
             \[{{40}^{o}}C\]                     done clear
  B)
             \[-{{10}^{o}}C\] done clear
  C)
             \[{{10}^{o}}C\]                     done clear
  D)
             \[{{0}^{o}}C\] done clear
  View Solution play_arrow

• question_answer24)
  On heating one end of a rod, the temperature of whole rod will be uniform when
  A)
             K = 1                                         done clear
  B)
             K = 0 done clear
  C)
             K = 100                                     done clear
  D)
             \[K=\infty \] done clear
  View Solution play_arrow

• question_answer25)
  Snow is more heat insulating than ice, because
  A)
             Air is filled in porous of snow done clear
  B)
             Ice is more bad conductor than snow done clear
  C)
             Air is filled in porous of ice done clear
  D)
             Density of ice is more done clear
  View Solution play_arrow

• question_answer26)
  Two thin blankets keep more hotness than one blanket of thickness equal to these two. The reason is
  A)
             Their surface area increases done clear
  B)
             A layer of air is formed between these two blankets, which is bad conductor done clear
  C)
             These have more wool done clear
  D)
             They absorb more heat from outside done clear
  View Solution play_arrow

• question_answer27)
  Ice formed over lakes has
  A)
             Very high thermal conductivity and helps in further ice formation done clear
  B)
             Very low conductivity and retards further formation of ice done clear
  C)
             It permits quick convection and retards further formation of ice done clear
  D)
             It is very good radiator done clear
  View Solution play_arrow

• question_answer28)
  Two rods of same length and material transfer a given amount of heat in 12 seconds, when they are joined end to end. But when they are joined lengthwise, then they will transfer same heat in same conditions in [BHU 1998; UPSEAT 2002]
  A)
             24 s                                           done clear
  B)
             3 s done clear
  C)
             1.5 s                                          done clear
  D)
             48s done clear
  View Solution play_arrow

• question_answer29)
  Wires A and B have identical lengths and have circular cross-sections. The radius of A is twice the radius of B \[i.e.\] \[{{r}_{A}}=2{{r}_{B}}\]. For a given temperature difference between the two ends, both wires conduct heat at the same rate. The relation between the thermal conductivities is given by
  A)
             \[{{K}_{A}}=4{{K}_{B}}\]  done clear
  B)
             \[{{K}_{A}}=2{{K}_{B}}\] done clear
  C)
             \[{{K}_{A}}={{K}_{B}}/2\] done clear
  D)
             \[{{K}_{A}}={{K}_{B}}/4\] done clear
  View Solution play_arrow

• question_answer30)
  Two identical plates of different metals are joined  to form a single plate whose thickness is double the thickness of each plate. If the coefficients of conductivity of each plate are  2 and 3 respectively, then the conductivity of composite plate will be
  A)
             5     done clear
  B)
             2.4 done clear
  C)
             1.5  done clear
  D)
             1.2 done clear
  View Solution play_arrow

• question_answer31)
  If the radius and length of a copper rod are both doubled, the rate of flow of heat along the rod increases
  A)
             4 times                                    done clear
  B)
             2 times done clear
  C)
             8 times                                    done clear
  D)
             16 times done clear
  View Solution play_arrow

• question_answer32)
  The coefficients of thermal conductivity of copper, mercury and glass are respectively Kc, Km and Kg such that Kc > Km > Kg. If the same quantity of heat is to  flow per second per unit area of each and corresponding temperature gradients are Xc, Xm and Xg, then                                            [MP PMT 1990]
  A)
             \[{{X}_{c}}={{X}_{m}}={{X}_{g}}\]                                    done clear
  B)
             \[{{X}_{c}}>{{X}_{m}}>{{X}_{g}}\] done clear
  C)
             \[{{X}_{c}}<{{X}_{m}}<{{X}_{g}}\]                                    done clear
  D)
             \[{{X}_{m}}<{{X}_{c}}<{{X}_{g}}\] done clear
  View Solution play_arrow

• question_answer33)
  If two metallic plates of equal thicknesses 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 this plate will be    [MP PMT 1991]
  A)
             \[\frac{{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]      done clear
  B)
             \[\frac{2{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\] done clear
  C)
             \[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{{{K}_{1}}{{K}_{2}}}\]          done clear
  D)
             \[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{2{{K}_{1}}{{K}_{2}}}\] done clear
  View Solution play_arrow

• question_answer34)
  The quantity of heat which crosses unit area of a metal plate during  conduction depends  upon [MP PMT 1992; JIPMER 1997]
  A)
             The density of the metal done clear
  B)
             The temperature gradient perpendicular to the area done clear
  C)
             The temperature to which the metal is heated done clear
  D)
             The area of the metal plate done clear
  View Solution play_arrow

• question_answer35)
  The ends of two rods of different materials with their thermal conductivities, radii of cross-sections and lengths all are in the ratio 1 : 2 are maintained  at the same temperature difference. If the rate of flow of heat in the larger rod is 4 \[4\ cal/\sec \], that in the shorter rod in \[cal/\sec \] will be [EAMCET 1986]
  A)
             1     done clear
  B)
             2 done clear
  C)
             8     done clear
  D)
             16 done clear
  View Solution play_arrow

• question_answer36)
  Two spheres of different materials one with double the radius and one-fourth wall thickness of the other, are filled with ice. If the time taken for complete melting ice in the large radius one is 25 minutes and that for smaller one is 16 minutes, the ratio of thermal conductivities of the materials of larger sphere to the smaller sphere is [EAMCET 1991]
  A)
             4 : 5                                           done clear
  B)
             5 : 4 done clear
  C)
             25 : 1                                         done clear
  D)
             1 : 25 done clear
  View Solution play_arrow

• question_answer37)
  The ratio of the diameters of two metallic rods of the same material is 2 : 1 and their lengths are in the ratio 1 : 4. If the temperature difference between their ends are equal, the rate of flow of heat in them will be in the ratio [MP PET 1994]
  A)
             2 : 1                                           done clear
  B)
             4 : 1 done clear
  C)
             \[8:1\]                                      done clear
  D)
             16 : 1 done clear
  View Solution play_arrow

• question_answer38)
  Two cylinders P and Q have the same length and diameter and are made of different materials having thermal conductivities in the ratio 2 : 3. These two cylinders are combined to make a cylinder. One end of P is kept at 100°C  and another end of Q at 0°C. The temperature at the interface of P and Q is        [MP PMT 1994; EAMCET 2000]
  A)
             \[{{30}^{o}}C\]                     done clear
  B)
             \[{{40}^{o}}C\] done clear
  C)
             \[{{50}^{o}}C\]                     done clear
  D)
             \[{{60}^{o}}C\] done clear
  View Solution play_arrow

• question_answer39)
  Two identical rods of copper and iron are coated with wax uniformly. When one end of each is kept at temperature of boiling water, the length upto which wax melts are \[8.4cm\] and \[4.2cm\] respectively. If thermal conductivity of copper is 0.92, then thermal conductivity of iron is [MP PET 1995]
  A)
             0.23                                           done clear
  B)
             0.46 done clear
  C)
             0.115                                        done clear
  D)
             0.69 done clear
  View Solution play_arrow

• question_answer40)
  Mud houses are cooler in summer and warmer in winter because            [BVP 2003]
  A)
             Mud is superconductor of heat done clear
  B)
             Mud is good conductor of heat done clear
  C)
             Mud is bad conductor of heat done clear
  D)
             None of these done clear
  View Solution play_arrow

• question_answer41)
  The temperature of hot and cold end of a \[20cm\] long rod in thermal steady state are at \[{{100}^{o}}C\] and \[{{20}^{o}}C\] respectively. Temperature at the centre of the rod is      [MP PMT 1996]
  A)
             \[{{50}^{o}}C\]                     done clear
  B)
             \[{{60}^{o}}C\] done clear
  C)
             \[{{40}^{o}}C\]                     done clear
  D)
             \[{{30}^{o}}C\] done clear
  View Solution play_arrow

• question_answer42)
  Two bars of thermal conductivities K and 3K and lengths \[1cm\] and \[2cm\] respectively have equal cross-sectional area, they are joined lengths wise as shown in the figure. If the temperature at the ends of this composite bar is \[{{0}^{o}}C\] and \[{{K}^{2}}/l\] respectively (see figure), then the temperature \[\varphi \]of the interface is
  A)
             \[{{50}^{o}}C\]                     done clear
  B)
             \[\frac{100}{3}{{\ }^{o}}C\] done clear
  C)
             \[{{60}^{o}}C\]                     done clear
  D)
             \[\frac{200}{3}{{\ }^{o}}C\] done clear
  View Solution play_arrow

• question_answer43)
  A heat flux of \[4000\ J/s\] is to be passed through a copper rod of length \[10\ cm\] and area of cross-section \[100\ c{{m}^{2}}\]. The thermal conductivity of copper is \[400\ W/m{{\ }^{o}}C\]. The two ends of this rod must be kept at a temperature difference of                                [MP PMT 1999]
  A)
             \[{{1}^{o}}C\]                       done clear
  B)
             \[{{10}^{o}}C\] done clear
  C)
             \[{{100}^{o}}C\]                   done clear
  D)
             \[{{1000}^{o}}C\] done clear
  View Solution play_arrow

• question_answer44)
   On a cold morning, a metal surface will feel colder to touch than a wooden surface because [AIIMS 1998]
  A)
             Metal has high specific heat done clear
  B)
             Metal has high thermal conductivity done clear
  C)
             Metal has low specific heat done clear
  D)
             Metal has low thermal conductivity done clear
  View Solution play_arrow

• question_answer45)
  In order that the heat flows from one part of a solid to another part, what is required [Pb. PMT 1999; EAMCET 1998]
  A)
             Uniform density                  done clear
  B)
             Density gradient done clear
  C)
             Temperature gradient      done clear
  D)
             Uniform temperature done clear
  View Solution play_arrow

• question_answer46)
  At a common temperature, a block of wood and a block of metal feel equally cold or hot. The temperatures of block of wood and block of metal are                                                                 [AIIMS 1999]
  A)
             Equal to temperature of the body done clear
  B)
             Less than the temperature of the body done clear
  C)
             Greater than temperature of the body done clear
  D)
             Either (b) or (c) done clear
  View Solution play_arrow

• question_answer47)
  According to the experiment of Ingen Hausz the relation between the thermal conductivity of a metal rod is K  and the length of the rod whenever the wax melts is  [UPSEAT 1999]
  A)
             K/l  = constant                      done clear
  B)
             \[{{K}^{2}}/l\]= constant done clear
  C)
             \[K/{{l}^{2}}\]= constant  done clear
  D)
             \[Kl\]= constant done clear
  View Solution play_arrow

• question_answer48)
  Temperature of water at the surface of lake is \[-{{20}^{o}}C.\]Then temperature of water just below the lower surface of ice layer is                                                      [RPET2000]
  A)
             \[-{{4}^{o}}C\]                      done clear
  B)
             \[{{0}^{o}}C\] done clear
  C)
             \[{{4}^{o}}C\]                       done clear
  D)
             \[-{{20}^{o}}C\] done clear
  View Solution play_arrow

• question_answer49)
  One end of a metal rod of length 1.0 m and area of cross section \[100c{{m}^{2}}\] is maintained at \[{{100}^{o}}C.\]If the other end of the rod is maintained at \[{{0}^{o}}C\], the quantity of heat transmitted through the rod per minute is (Coefficient of thermal conductivity of material of rod =100W/m-K) [EAMCET (Engg.) 2000]
  A)
             \[3\times {{10}^{3}}J\]      done clear
  B)
             \[6\times {{10}^{3}}J\] done clear
  C)
             \[9\times {{10}^{3}}J\]      done clear
  D)
             \[12\times {{10}^{3}}J\] done clear
  View Solution play_arrow

• question_answer50)
  The coefficient of thermal conductivity of copper is nine times that of steel. In the composite cylindrical bar shown in the figure. What will be the temperature at the junction of copper and steel                      [MP PMT 2000; BHU 2004]
  A)
             \[{{75}^{o}}C\] done clear
  B)
             \[{{67}^{o}}C\] done clear
  C)
             \[{{33}^{o}}C\] done clear
  D)
             \[{{25}^{o}}C\] done clear
  View Solution play_arrow

• question_answer51)
  The lengths and radii of two rods made of same material are in the ratios 1 : 2 and 2 : 3 respectively. If the temperature difference between the ends for the two rods be the same, then in the steady state, the amount of heat flowing per second through them will be in the ratio          [MP PET 2000]
  A)
              1: 3                                           done clear
  B)
             4 : 3 done clear
  C)
             8 : 9                                           done clear
  D)
             3 : 2 done clear
  View Solution play_arrow

• question_answer52)
  A slab consists of two parallel layers of two different materials of same thickness having thermal conductivities K1 and K2. The equivalent conductivity of the combination is  [BHU 2001]
  A)
             \[{{K}_{1}}+{{K}_{2}}\]      done clear
  B)
             \[\frac{{{K}_{1}}+{{K}_{2}}}{2}\] done clear
  C)
             \[\frac{2{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]   done clear
  D)
             \[\frac{{{K}_{1}}+{{K}_{2}}}{2{{K}_{1}}{{K}_{2}}}\] done clear
  View Solution play_arrow

• question_answer53)
  There are two identical vessels filled with equal amounts of ice. The vessels are of different metals., If the ice melts in the two vessels in 20 and 35 minutes respectively, the ratio of the coefficients of thermal conductivity of the two metals is  [AFMC 1998; MP PET 2001]
  A)
             4 : 7                                           done clear
  B)
             7 : 4 done clear
  C)
             16 :49                                       done clear
  D)
             49 : 16 done clear
  View Solution play_arrow

• question_answer54)
  Surface of the lake is at 2°C. Find the temperature of the bottom of the lake                                       [Orissa JEE 2002]
  A)
             \[{{2}^{o}}C\]                       done clear
  B)
             \[{{3}^{o}}C\] done clear
  C)
             \[{{4}^{o}}C\]                       done clear
  D)
             \[{{1}^{o}}C\] done clear
  View Solution play_arrow

• question_answer55)
  The heat is flowing through a rod of length 50 cm and area of cross-section \[5c{{m}^{2}}\]. Its ends are respectively at \[{{25}^{o}}C\] and \[{{125}^{o}}C\]. The coefficient of thermal conductivity of the material of the rod is 0.092 kcal/m×s×oC. The temperature gradient in the rod is                                      [MP PET 2002]
  A)
             \[{{2}^{o}}C/cm\]               done clear
  B)
             \[{{2}^{o}}C/m\] done clear
  C)
             \[{{20}^{o}}C/cm\]             done clear
  D)
             \[{{20}^{o}}C/m\] done clear
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• question_answer56)
  In the Ingen Hauz?s experiment the wax melts up to lengths 10 and 25 cm on two identical rods of different materials. The ratio of thermal conductivities of the two materials is  [MP PET 2002]
  A)
             \[1:6.25\]                                done clear
  B)
             6.25 : 1 done clear
  C)
             \[1:\sqrt{2.5}\]                     done clear
  D)
             1 : 2.5 done clear
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• question_answer57)
  Heat current is maximum in which of the following (rods are of identical dimension) [Orissa JEE 2003]
  A)
                                        done clear
  B)
                                   done clear
  C)
                                          done clear
  D)
    done clear
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• question_answer58)
             Two rods of same length and cross section are joined along the length. Thermal conductivities of first and second rod are \[{{K}_{1}}\,\,\text{and}\,\,{{K}_{2}}\]. The temperature of the free ends of the first and second rods are maintained at \[{{\theta }_{1}}\,\,\text{and }{{\theta }_{2}}\] respectively. The temperature of the common junction is   [MP PET 2003]
  A)
             \[\frac{{{\theta }_{1}}+{{\theta }_{2}}}{2}\]                done clear
  B)
             \[\frac{{{K}_{2}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}({{\theta }_{1}}+{{\theta }_{2}})\] done clear
  C)
             \[\frac{{{K}_{1}}{{\theta }_{1}}+{{K}_{2}}{{\theta }_{2}}}{{{K}_{1}}+{{K}_{2}}}\]       done clear
  D)
             \[\frac{{{K}_{2}}{{\theta }_{1}}+{{K}_{1}}{{\theta }_{2}}}{{{K}_{1}}+{{K}_{2}}}\] done clear
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• question_answer59)
  Consider a compound slab consisting of two different materials having equal thickness and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is                          [CBSE PMT 2003]
  A)
             \[\sqrt{2K}\]                         done clear
  B)
             \[3K\] done clear
  C)
             \[\frac{4}{3}K\]                    done clear
  D)
             \[\frac{2}{3}K\] done clear
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• question_answer60)
  Two rods having thermal conductivity in the ratio of 5 : 3 having equal lengths and equal cross-sectional area are joined by face to face. If the temperature of the free end of the first rod is 100oC and free end of the second rod is 20oC. Then temperature of the junction is [CPMT 1996; DPMT 1997, 03; BVP 2004]
  A)
             70 o C                                        done clear
  B)
             50 o C done clear
  C)
             50 o C                                        done clear
  D)
             90 o C done clear
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• question_answer61)
  Woollen clothes are used in winter season because woolen clothes        [EAMCET 1978; AIIMS 1998]
  A)
             Are good sources for producing heat done clear
  B)
             Absorb heat from surroundings done clear
  C)
             Are bad conductors of heat done clear
  D)
             Provide heat to body continuously done clear
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• question_answer62)
  Two metal cubes \[A\] and \[B\] of same size are arranged as shown in the figure. The extreme ends of the combination are maintained at the indicated temperatures. The arrangement is thermally insulated. The coefficients of thermal conductivity of \[A\] and \[B\] are \[300\ W/m{{\ }^{o}}C\] and \[200\ W/m{{\ }^{o}}C\], respectively. After steady state is reached, the temperature of the interface will be              [IIT 1996]
  A)
             \[{{45}^{o}}C\]  done clear
  B)
             \[{{90}^{o}}C\] done clear
  C)
             \[{{30}^{o}}C\] done clear
  D)
             \[{{60}^{o}}C\] done clear
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• question_answer63)
  A cylindrical rod having temperature \[{{T}_{1}}\] and \[{{T}_{2}}\] at its ends. The rate of flow of heat is \[{{Q}_{1}}\]cal/sec. If all the linear dimensions are doubled keeping temperature constant then rate of flow of heat \[{{Q}_{2}}\]will be                        [CBSE PMT 2001]                        
  A)
             \[4{{Q}_{1}}\]                       done clear
  B)
             \[2{{Q}_{1}}\] done clear
  C)
             \[\frac{{{Q}_{1}}}{4}\]       done clear
  D)
             \[\frac{{{Q}_{1}}}{2}\] done clear
  View Solution play_arrow

• question_answer64)
  A body of length 1m having cross sectional area 0.75m2 has heat flow through it at the rate of 6000 Joule/sec. Then find the temperature difference if \[K=200J{{m}^{-1}}{{K}^{-1}}\] [CPMT 2001]      
  A)
             20°C                                          done clear
  B)
             40°C done clear
  C)
             80°C                                          done clear
  D)
             100°C done clear
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• question_answer65)
  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                                                                       [CPMT 1998]
  A)
             The temperature difference across \[A=15{}^\circ C\] done clear
  B)
             The temperature difference across \[A=5{}^\circ C\] done clear
  C)
             The temperature difference across A is 10°C done clear
  D)
             The rate of transfer of heat through A is more than that through B. done clear
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• question_answer66)
  A metal rod of length 2m has cross sectional areas 2A and A as shown in figure. The ends are maintained at temperatures 100°C and 70°C. The temperature at middle point C is  [CPMT 2000]
  A)
             80°C done clear
  B)
             85°C done clear
  C)
             90°C done clear
  D)
             95°C done clear
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• question_answer67)
  The ratio of the coefficient of thermal conductivity of two different materials is 5 : 3. If the thermal resistance of the rod of same thickness resistance of the rods of same thickness of these materials is same, then the ratio of the length of these rods will be                                                      [BHU 2000]
  A)
             3 : 5                                           done clear
  B)
             5 : 3 done clear
  C)
             3 : 4                                           done clear
  D)
              3 : 2 done clear
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• question_answer68)
  Which of the following circular rods. (given radius r and length l) each made of the same material as whose ends are maintained at the same temperature will conduct most heat                                                                       [CBSE PMT 2005]
  A)
             \[r=2{{r}_{0}};\ l=2{{l}_{0}}\]  done clear
  B)
             \[r=2{{r}_{0}};\ l={{l}_{0}}\] done clear
  C)
             \[r={{r}_{0}};\ l={{l}_{0}}\]      done clear
  D)
             \[r={{r}_{0}};\ l=2{{l}_{0}}\] done clear
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