4

# Depending on the radiating properties, a body will be opaque when

P = 0, x = 0 and a = 1

P=1, x = 0 and a = 0

P = 0, x = 1 and a = 0

X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.

D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.

4

# The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

First law of thermodynamics

Newton's law of cooling

Newton's law of heating

Stefan's law

4

Emissivity

Transmissivity

Reflectivity

4

# When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Conduction

Convection

Conduction and convection

4

# The use of heat exchangers is made in

Condensers and boilers in steam plants

Condensers and evaporators in refrigeration and air conditioning units

All of the above

4

# According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

4

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

4

Maximum

Minimum

Zero

None of these

4

K cal/kg m² °C

K cal m/hr m² °C

K cal/hr m² °C

K calm/hr °C

4

# The critical temperature is the temperature

Below which a gas does not obey gas laws

Above which a gas may explode

Below which a gas is always liquefied

Above which a gas will never liquefied

4

Kirchoffs law

Stefan's law

Wien' law

Planck's law

4

# The heat transfer takes place according to

Zeroth law of thermodynamics

First law of thermodynamics

Second law of thermodynamics

Kirchhoff's law

4

# According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

Grey body

Brilliant white polished body

Red hot body

Black body

4

# Pick up the wrong case. Heat flowing from one side to other depends directly on

Face area

Time

Thickness

Temperature difference

4

Grashoff number

Biot number

Stanton number

Prandtl number

4

6

9

27

81

4

# Sensible heat is the heat required to

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid of vapour

Convert water into steam and superheat it

4

# Heat transfer in liquid and gases takes place by

Conduction

Convection

Conduction and convection

4

# Film coefficient is defined as the ratio of

Thermal conductivity to the equivalent thickness of the film of fluid

Temperature drop through the films of fluids to the thickness of film of fluids

Thickness of film of fluid to the thermal conductivity

Thickness of film of fluid to the temperature drop through the films of fluids

4

-1/3

-2/3

1

-1

4

Thermometer

Thermistor

Thermocouple

None of these

4

# Free convection flow depends on

Density

Coefficient of viscosity

Gravitational force

All of these

4

# In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Convection

Conduction

Both convection and conduction

4

# Emissivity of a white polished body in comparison to a black body is

Higher

Lower

Same

Depends upon the shape of body

4

# A steam pipe is to be insulated by two insulating materials put over each other. For best results

Better insulation should be put over pipe and better one over it

Inferior insulation should be put over pipe and better one over it

Both may be put in any order

Whether to put inferior OIL over pipe or the better one would depend on steam temperature

4

Steam

Solid ice

Melting ice

Water

4

0.1

0.3

0.7

1.7

4

0

0.5

0.75

1

4

# Depending on the radiating properties, body will be transparent when

P = 0, x = 0 and a = 1

P=1, x = 0, and a = 0

P = 0, T= 1, and a = 0

X = 0, a + p = 1

4

# According to Wien's law, the wavelength corresponding to maximum energy is proportion to

Absolute temperature (T)

F

T