Heat Objective Type Questions & Answers

Questions

21 Metals are good conductors of heat because

A their atoms collide frequently

B their atoms-are relatively far apart

C they contain free electrons

D they have high density

View Answer

Answer: their atoms collide frequently

22 Total heat is the heat required to

A change vapour into liquid

B change liquid into vapour

C increase the temperature of a liquid or vapour

D convert water into steam and superheat it

View Answer

Answer: convert water into steam and superheat it

23 Thermal conductivity of water at 20°C is of the order of

A 0.1

B 0.23

C 0.42

D 0.51

View Answer

Answer: 0.51

24 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

View Answer

Answer: the time taken to attain 63.2% of the value of initial temperature difference

25 Heat flows from one body to other when they have

A different heat contents

B different specific heat

C different atomic structure

D different temperatures

View Answer

Answer: different temperatures

26 In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by

A hr (time)

B sqm (area)

C °C (temperature)

D cm (thickness)

View Answer

Answer: cm (thickness)

27 Which of the following has least value of conductivity

A glass

B water

C plastic

D air

View Answer

Answer: air

28 Which of the following is expected to have highest thermal conductivity

A steam

B solid ice

C melting ice

D water

View Answer

Answer: solid ice

29 Thermal conductivity of glass-wool varies from sample to sample because of variation in

A composition

B density

C porosity

D all of the above

View Answer

Answer: all of the above.

30 Which of the following has maximum value of thermal conductivity

A aluminium

B steel

C brass

D copper

View Answer

Answer: aluminium

31 Moisture would find its way into insulation by vapour pressure unless it is prevented by

A high thickness of insulation

B high vapour pressure

C less thermal conductivity insulator

D a vapour seal

View Answer

Answer: a vapour seal

32 The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj - 2K2 will be

A I

B 0.5

C 2

D 0.25

View Answer

Answer: 2

33 Thermal diffusivity is

A a dimensionless parameter

B function of temperature

C used as mathematical model

D a physical property of the material

View Answer

Answer: a physical property of the material

34 Unit of thermal diffusivity is

A m2/hr

B m2/hr°C

C kcal/m2 hr

D kcal/m.hr°C

View Answer

Answer: m2/hr

35 Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called

A thermal resistance

B thermal coefficient

C temperature gradient

D thermal conductivity

View Answer

Answer: thermal conductivity

36 A grey body is one whose absorptivity

A varies with temperature

B varies with wavelength of the incident ray

C is equal to its emissivity

D does not vary with temperature and. wavelength of the incident ray

View Answer

Answer: is equal to its emissivity

37 A non-dimensional number generally associated with natural convection heat transfer is

A Grashoff number

B Nusselt number

C Weber number

D Prandtl number

View Answer

Answer: Grashoff number

38 In counter flow heat exchangers

A both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state

B both the fluids at inlet are in their hot¬test state

C both the fluids .at exit are in their hottest state

D one fluid is in hottest state and other in coldest state at inlet

View Answer

Answer: both the fluids at inlet are in their hot¬test state

39 Fourier's law of heat conduction is valid for

A one dimensional cases only

B two dimensional cases only

C three dimensional cases only

D regular surfaces having non-uniform temperature gradients

View Answer

Answer: one dimensional cases only

40 All radiations in a black body are

A reflected

B refracted

C transmitted

D absorbed

View Answer

Answer: absorbed

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