Heat Quiz | Heat Objective Type Questions & Answers

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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

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

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

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

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

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)

Answer: cm (thickness)
27 Which of the following has least value of conductivity
A glass
B water
C plastic
D air

Answer: air
28 Which of the following is expected to have highest thermal conductivity
A steam
B solid ice
C melting ice
D water

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

Answer: all of the above.
30 Which of the following has maximum value of thermal conductivity
A aluminium
B steel
C brass
D copper

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

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

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

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

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

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

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

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

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

Answer: one dimensional cases only
40 All radiations in a black body are
A reflected
B refracted
C transmitted
D absorbed

Answer: absorbed
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