Mechanical Engineering Mcqs

According to Prevost theory of heat exchange ___________________?
  • (A)  it is impossible to transfer heat from low temperature source to t high temperature source
  • (B)  heat transfer by radiation requires no medium
  • (C)  all bodies above absolute zero emit radiation
  • (D)  heat transfer in most of the cases takes place by combination of conduction, convection and radiation
  • (E)  rate of heat transfer depends on thermal conductivity and temperature difference
Thermal conductivity of a material may be defined as the________________?
  • (A)  quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
  • (B)  quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
  • (C)  heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
  • (D)  all of the above
  • (E)  none of the above
The time constant of a thermocouple is_______________?
  • (A)  the time taken to attain the final temperature to be measured
  • (B)  the time taken to attain 50% of the value of initial temperature difference
  • (C)  the time taken to attain 63.2% of the value of initial temperature difference
  • (D)  determined by the time taken to reach 100°C from 0°C
  • (E)  none of the above