Q.1
Four rods of same material are taken. the length l and radius of cross-section r are given below. In which rod the heat flow will be maximum when temperature difference across the end rods is same under steady state? [ MPPMT 1987]
  • a)l=50 cm, r=0.5 cm
  • b) l=100 cm, r=1.0 cm
  • c)l=75 cm, r=1.5 cm
  • d)l=100 cm, r=2.0 cm
Q.2
Solar radiation emitted by sun resembles that emitted by a black body at a temperature of 6000K. Maximum intensity is emitted at wave length of about 4800 Å. if the sun were to cool down from 6000K to 3000K, then the peak intensity would occur at a wave length [ MPPMT 1991]
  • a) 4800
  • b) 9600
  • c)2400
  • d)19200
Q.3
Equal temperature difference exists between the ends of two metallic rods 1 and 2 of equal length. their thermal conductivity is K1 and K2 and cross-sectional areas are respectively A1 and AThe condition for equal rate of heat transfer will be [ MPPMT 1991]
  • a) K1 / A1=K2/A2
  • b) K1 A22=K2 A12
  • c) K1 A1=K2 A2
  • d) K1 A12=K2 A22
Q.4
The speediest mode of heat transfer is [ MPPMT 1994]
  • a)conduction
  • b) convection
  • c)radiation
  • d)combustion
Q.5
The coefficient 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 sec unit area of each and corresponding temperature gradients are Xc,Xm and Xg[ MPPMT 1990]
  • c)Xc < Xm < Xg
  • a) Xc=Xm=Xg
  • b) Xc > Xm > Xg
  • d)Xm < Xc < Xb
Q.6
Ice starts forming in a lake with water at 0°C, when the atmospheric temperature is -10°C. If the time taken for 1cm of ice to be formed in 7 hrs, the time taken for the thickness of ice to change from 1cm to 2 cm is [ MPPT 1988]
  • a) 7 hours
  • b) Less than 7 hours
  • c)more than 7 hours but less than 14 hours
  • d)more than 14 hours
Q.7
A wall has two layers A and B each made of different material. Both the layers have the same thickness. The thermal conductivity of the material of A is twice that of B. Under thermal equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is [ IIT 1980]
  • a) 6°C
  • b) 12°C
  • c) 18°C
  • d) 24°C
Q.8
A piece of blue glass heated to high temperature and piece of red glass at room temperature are taken inside a dim-light room then
  • a)the blue piece will look blue and the red piece will look red as usual
  • b) the red piece will look brighter red and the blue piece will look ordinary blue
  • c)the blue piece will look brighter as compared to the red piece
  • d)both the pieces will look equally red
Q.9
A cylinder of radius R made of a material of thermal conductivity K1 is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of material of thermal conductivity KThe 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 [ IIT 1988]
  • a) K1 + K2
  • b) K1 K2 / ( K1 + K2)
  • c)(K1 + 3K2 ) /4
  • d)(3K1 + K2) / 4
Q.10
For a perfectly black body, its absorptive power is [ MPPMT 1989]
  • a) 1
  • b) 0.5
  • c)0.8
  • d)2.0
Q.11
Two idential 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 8.4 cm and 4.2cm, respectively. If thermal condutiuvity of copper is 0.92, then thermal concutivity of iron rod is [ MPPMT 1995]
  • a) 0.23
  • b) 0.46
  • c) 0.115
  • d) .69
Q.12
Which of the following combinations of properties would be most desirable for cooking pot [ MPPMT 1995]
  • a)high specific heat and low conductivity
  • b) low specific heat and high conductivity
  • c)high specific heat and high conductivity
  • d)low specific heat and low conductivity
Q.13
At a certain temperature for given wave length, the ratio of emmissive power of a body to emissive power of black body in same circumstances is known as [ Raj. PMT 1997]
  • a) Relative emissivity
  • b) Emissivity
  • c)Absorption coefficient
  • d)Coefficient of reflection
Q.14
A object is at temperature of 400°C. At what temperature would it radiate energy twice as fast? The temperature of the surroundings may be assumed to be negligible [ MPPT 1990]
  • a) 200 °C
  • b) 200K
  • c)800°C
  • d)800 K
Q.15
A piece of glass is heated to 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
  • b) high thermal conductivity
  • c) high specific heat
  • d) high melting point
Q.16
Certain substance emits only the wave lengths λ1, λ2, λ3 and λ4 when it is at high temperature. When this substance is at a colder temperature it will absorb only the following wave lengths [ PET 1990]
  • a)λ1
  • b) λ1 and λ2
  • c)λ2
  • d)λ1, λ2, λ3 and λ4
Q.17
Two stars A and B radiate maximum energy at 3600Å and 4800Å respectively. Then the ratio of absolute temperature of A and B is [ MPPMT 1991]
  • a) 4 : 3
  • b) 3 : 4
  • c)256 : 81
  • d)81 : 256
Q.18
Two walls of thickness d1 and d2 and thermal condutivities k1 and k2 are in contact. in the steady state, if the temperatures at the outer surface are T1 and TThe temperature at the common wall is [ CPMT 1998]
  • a)
    ch-8_qn-227choice_img_no1.png
  • b)
    ch-8_qn-227choice_img_no2.png
  • c)
    ch-8_qn-227choice_img_no3.png
  • d)
    ch-8_qn-227choice_img_no4.png
Q.19
The ends of two rods of different materials with their thermal conductivities, radii of cross-sections and lengths all are in ratio 1 : 2 are maintained at the same temperature difference. If the rate of flow of heat in the larger rod is 4 cal/sec, then in the shorter rod in cal/sec will be [ EAMCET 1986]
  • a) 1
  • b) 2
  • c) 8
  • d) 16
Q.20
A cylindrical rod with one in a steam chamber and the other end in ice results in melting of 0.1gm of ice per second. If the rod is replaced by another with half the length and double the radius of the first and if the thermal conductivity of material of second rod is (1/4) that of first, the rate at which ice melts in gm/sec will be [ EAMCET 1987]
  • a)3.2
  • b) 1.6
  • c)0.2
  • d)0.1
Q.21
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 of ice in the larger radius one is 25 minutes and that for smaller one in 16 minutes, the ratio of thermal conductivities of the materials of larger sphere to the smaller sphere is [ EAMCET 1991]
  • a) 4 : 5
  • b) 5 : 4
  • c)25 : 8
  • d)8 : 25
Q.22
One end of a copper rod of length 1.0m and area of cross-section 10-3 m2 is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is 92 cal/m/s/°C and the latent heat of ice is 8×104 cal/kg, then the amount of ice which will melt in one minute is [ MNR 1994]
  • a) 9.2 × 10-3 kg
  • b) 8 × 10-3 kg
  • c) 6.9 × 10-3 kg
  • d) 5.4 × 10-3 kg
Q.23
Which of the following statement is wrong [ MPPMT 1993]
  • a) Stefan's constant is the same for all black bodies
  • b) Thermal radiations travel with the speed of 3×108 m/s
  • c) Thermal radiations exhibits diffraction
  • d) Stefan's law is applicable for all heated bodies
Q.24
A sphere, a cube and a thin circular plate all made of the same material and having the same mass are heated to the same temperature of 200°C when these are left in room [ MPPMT 1993]
  • a) the sphere reaches room temperature last
  • b) the cube reaches room temperature last
  • c) the circular plate reaches room temperature last
  • d) all will reach the room temperature simultaneously
Q.25
A piece of metal and a piece of wood are kept in a room at room temperature which is 45°C. On touching the two with hand [ MPPET 1993]
  • a) the two will appear equally hot
  • b) the piece of wood will appear hotter than the piece of metal
  • c) the piece of metal will appear hotter than the piece of wood
  • d) the distinction in the hotness will not be possible
Q.26
An electric heater, kept in vacuum is heated continuously by passing electric current. Its temperature will [ MPPMT 1993]
  • a) go on rising with time
  • b) stop rising after some time as it will lose heat to the surrounding by conduction
  • c) will rise for some time and thereafter will start falling
  • d) will become constant after some time due to loss of heat by radiation
Q.27
At specific temperature, the energy densities for 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 power of this body for these wave-lengths are in the ratio
  • a) 10 : 19 : 7
  • b) 8 : 3 : 9
  • c) 8 : 5.7 : 6.3
  • d) 8 : 95 : 4.3
Q.28
On investigation of light from three different stars A, B, and C it was found that in the spectrum of A, the intensity of red colour is maximum, in B, the intensity of blue colour is maximum. and in C the intensity of yellow colour is maximum. From these observations it can be concluded that [ CPMT 1989]
  • a) the temperature of A is maximum, B is minimum and C is intermediate
  • b) the temperature of A is maximum, C is minimum and B is intermediate
  • c) the temperature of B is maximum, A is minimum and C is intermediate
  • d) the temperature of C is maximum, B is minimum and A is intermediate
Q.29
A blackened metal foil is warmed by radiation from a point source whose temperature is T and distance from the foil is d. It is found that the power received from the foil is P. If both the temperature and distance are doubled, the power received by the foil will be [ MPPMT 1997]
  • a) P
  • b) 2P
  • c) 4P
  • d) 16P
Q.30
Three rods of identical area of cross-section and made from the same metal, from the sides of an isosceles triangle ABC, right-angled at B. The points A and B are maintained at temperature T and (√2) T, respectively. in the steady state, the temperature of the part C is Tc. Assuming that only heat conduction takes place Tc / T is [ IIT 1995]
  • a)
    ch-8_qn-239choice_img_no1.png
  • b)
    ch-8_qn-239choice_img_no2.png
  • c)
    ch-8_qn-239choice_img_no3.png
  • d)
    ch-8_qn-239choice_img_no4.png
0 h : 0 m : 1 s