If the radius of any current carrying conductor is less than the critical radius, then why the addition of electrical insulation will enable the wire to carry a higher current?
  • a) The heat loss from the wire would decrease
  • b) The heat loss from the wire would increase
  • c) The thermal resistance of the insulation is reduced
  • d) The thermal resistance of the conductor is increased
Which of the following substance has the minimum value of thermal conductivity?
  • a) Air
  • b) Water
  • c) Plastic
  • d) Rubber
In MLTθ system (T time and θ temperature), what is the dimension of thermal conductivity?
  • a) ML-1T-1θ-3
  • b) MLT-1θ-3
  • c) MLT-3θ-1
  • d) MLT-2θ-1
For conduction through a spherical wall with constant thermal conductivity and with inner side temperature greater than outer wall temperature in 1-D heat transfer, what is the type of temperature
  • a) Linear
  • b) Parabolic
  • c) Hyperbolic
  • d) Logarithmic
Which of the following expresses the thermal diffusivity of a substance in terms of thermal conductivity of a substance (k), mass density (ρ) and specific heat (c)?
  • a) k2ρc
  • b) 1/ρkc
  • c) k/ρc
  • d) ρc/k2
A copper block and an air mass block having similar dimensions are subjected to symmetrical heat transfer from one face of the each block. The other face of the block will be reaching to the same temperature at a rate?
  • a) Faster in air block
  • b) Faster in copper block
  • c) Equal in air as well as copper block
  • d) Data in sufficient
The outer surface of a long cylinder is maintained at constant temperature. The cylinder does not have any heat source. The temperatures in the cylinder will _________
  • a) Increase linearly with radius
  • b) Decrease linearly with radius
  • c) Be independent of radius
  • d) Vary logarithmically with radius
A steam pipe is covered with two layers of insulating materials, with the better insulating material forming the outer. What is the effect on heat conducted if the two layers are interchanged?
  • a) Will increase
  • b) Will decrease
  • c) Will remain unaffected
  • d) May increase or decrease depending upon the thickness of each layer
A plane wall is 20cm thick with an area perpendicular to heat flow of 1m2 and has a thermal conductivity of 0.5W/mK. A temperature difference of 100°C is imposed across it. What is the ratio of heat flow?
  • a) 0.10 kW
  • b) 0.15 kW
  • c) 0.20 kW
  • d) 0.25 kW
An insulating material with a thermal conductivity k = 0.12W/mK is used for a pipe carrying steam. The local coefficient of heat transfer to the surrounding h = 4 W/m2K. In order to provide effective insulation, what should be the minimum outer diameter of the pipe?
  • a) 45mm
  • b) 60mm
  • c) 75mm
  • d) 90mm
In a long cylindrical rod of radius R and a surface heat flux of qwhat is the uniform internal heat generation rate?
  • a) 2q0/R
  • b) 2q0
  • c) q0/R
  • d) 2q0/3R
A plane slab of 100mm thickness generates heat. It is observed that the temperature drop between the center and its surface to be 50°C. If the thickness is increased to 200mm the temperature difference will be ___________
  • a) 100°C
  • b) 200°C
  • c) 400°C
  • d) 600°C
As the temperature increases, the thermal conductivity of a gas ____________
  • a) Increases
  • b) Decreases
  • c) Remain constant
  • d) Increases up to a certain temperature and then decreases
0 h : 0 m : 1 s