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# Multiple choice question for engineering

## Set 1

1. Which of the followings is a wrong statement?
The shape factor is equal to one
a) For any surface completely enclosed by another surface
b) For infinite parallel planes radiating only to each other
c) For a flat or convex surface with respect to itself
d) Inside cylinder to outer cylinder of a long co-axial cylinder

Answer: d [Reason:] For a flat or convex surface, the shape factor with respect to itself is zero. This aspect stems from the fact that for any part of flat or convex surface, one cannot see any other part of the same surface.

2. Establish a relation for the shape factor of cylindrical cavity with respect to itself of depth h and diameter d. The cavity is closed on its outer surface with a flat plate a) 4 h/4 h + d
b) 4 h + d/h
c) 4 h + d/4 h
d) h/4 h + d

Answer: a [Reason:] F 11 + F 12 = 1 and F 21 + F 22 = 1. But F 22 = 0, so F 11 = 1 – A 2 / A 1.

3. The reciprocity theorem states that
a) F 12 = F 21
b) A 1 F 12 = A 2 F 21
c) A 1 F 21 = A 2 F 12
d) A 2 F 21 = A 1 F 12
Where symbols have their usual meanings

Answer: b [Reason:] It indicates the net radiation exchange can be calculated by computing one way configuration factor from either surface to the other.

4. Two radiating surface A 1 = 6 m2 and A 2 = 4 m2 have shape factor F 12 = 0.1. Then the shape factor F 21 will be
a) 0.12
b) 0.18
c) 0.15
d) 0.10

Answer: c [Reason:] A 1 F 12 = A 2 F 21.

5. What is the value of shape factor for two infinite parallel surfaces separated by a distance x?
a) 0
b) 1
c) x
d) Infinity

Answer: b [Reason:] All the radiation emitted by one falls on the other so shape factor is unity.

6. What is the shape factor of a sphere of diameter d inside a cubical box of length l = d? a) π/6
b) 2 π/6
c) π/3
d) π/4

Answer: a [Reason:] F 11 + F 12 = 1 or F 12 = 1. So, F 21 = π/6.

7. What is the shape factor of hemispherical surface closed by a plane surface of diameter d?
a) 0
b) 1.5
c) 1
d) 0.5

Answer: d [Reason:] F 11 + F 12 = 1 and F 21 = 1. Therefore, F 11 = 0.5.

8. Establish a relation for shape factor for a conical cavity with respect to itself of depth h and diameter d. The cavity is closed on its outer surface with a flat plate a) 1 – d/ (4 h 2 + d) 1/2
b) 1 – d/ (4 h 2 + d 2) 1/2
c) 1 – d/ (4 h + d 2) 1/2
d) 1 – d/ (h 2 + d 2) 1/2

Answer: b [Reason:] F 11 = 1 – A 2 / A 1 = 1 – 2 sin α = 1 – d/ (4 h 2 + d 2) ½.

9. What is the shape factor for a hemispherical bowl with respect to itself of diameter d? The cavity is closed on its outer surface with a flat plate
a) 1.5
b) 1
c) 0.5
d) 2.5

Answer: c [Reason:] F 11 = 1 – A 2 / A 1 = 0.5.

10. Consider a system of concentric spheres of radius r 1 and r 2 (r 2 is greater than r 1). If r 1 = 5 cm, determine the radius r 2 if it is desired to have the value of shape factor F 21 equal to 0.6 a) 6.45 cm
b) 7.45 cm
c) 8.45 cm
d) 9.45 cm

Answer: a [Reason:] From reciprocity theorem, A 1 F 12 = A 2 F 21.

## Set 2

1. Ratio of inertia force to viscous force is known as
a) Grashof number
b) Reynolds number
c) Peclet number
d) Stanton number

Answer: b [Reason:] It is given by p l v/µ. It is the indicative of the relative importance of inertial and viscous effects in a fluid motion.

2. The ratio of heat flow rate by convection to flow rate by conduction is known as
a) Stanton number
b) Graetz number
c) Fourier number
d) Peclet number

Answer: d [Reason:] It is given by I V/α. It is a function of Reynolds number and Prandtl number.

3. The ratio of heat capacity of fluid flowing through the pipe per unit of length to the conductivity of pipe material is known as
a) Graetz number
b) Reynolds number
c) Peclet number
d) Fourier number

Answer: a [Reason:] It is given by Pe (π d/4 l). It represents the ratio of heat capacity of fluid flowing through the pipe per unit of length to the conductivity of pipe material.

4. Identify the correct statement
a) Peclet number = (Graetz number) (Fourier number)
b) Peclet number = (Stanton number) (Fourier number)
c) Peclet number = (Reynolds number) (Prandtl number)
d) Peclet number = (Graetz number) (Reynolds number)

Answer: c [Reason:] Peclet number is a function of Reynolds number and Prandtl number. Peclet number = p c l V/ k = p l V/µ (µ c/k) = (Re) (Pr).

5. What is the value of Prandtl number for highly viscous oils?
a) 100-1000
b) 0-100
c) 10-100
d) 100-10000

Answer: d [Reason:] It indicates rapid diffusion of momentum by viscous action compared to the diffusion of energy.

6. What is the value of Prandtl number for liquid metals?
a) 0.003-0.01
b) 0.01-0.1
c) 0.1-0.5
d) 0.5-0.95

Answer: a [Reason:] It indicates more rapid diffusion of energy compared to the momentum diffusion rate.

7. The product of buoyant force and inertia force to the square of the viscous force is known as
a) Stanton number
b) Grashof number
c) Fourier number
d) Peclet number

Answer: b [Reason:] It indicates the relative strength of the buoyant to the viscous forces. It represents the ratio of the product of buoyant and inertia forces to the square of the viscous forces.

8. The ratio of heat transfer coefficient to the flow of heat per unit temperature rise due to the velocity of the fluid is known as
a) Fourier number
b) Grashof number
c) Peclet number
d) Stanton number

Answer: d [Reason:] Stanton number can be used in correlating forced convection data. This becomes obvious when we observe the velocity V contained in the expression of Stanton number. It is the ratio of heat transfer coefficient to the flow of heat per unit temperature rise due to the velocity of the fluid.

9. Which number indicates the relative ability of the fluid to diffuse momentum and internal energy by molecular mechanisms?
a) Nusselt number
b) Prandtl number
c) Peclet number
d) Stanton number

Answer: b [Reason:] It is the ratio of kinematic viscosity to thermal diffusivity of the fluid.

10. Which number establishes the relation between convective film coefficient, thermal conductivity of the fluid and a significant length parameter?
a) Nusselt number
b) Stanton number
c) Peclet number
d) Fourier number

Answer: a [Reason:] The Nusselt number may be interpreted as the ratio of temperature gradient to an overall reference temperature gradient.

## Set 3

1. Which one is having highest value of solar absorptivity?
a) White marble
b) Concrete
c) Asphalt
d) Snow

Answer: c [Reason:] Solar absorptivity for asphalt is 0.90 while that of white marble, concrete and snow are 0.46, 0.60 and 0.28 respectively.

2. What is the value of solar absorptivity for aluminum foil?
a) 0.15
b) 0.16
c) 0.17
d) 0.18

Answer: a [Reason:] Solar absorptivity doesn’t require a medium and for aluminum it reaches maximum efficiency in a vacuum.

3. What is the value of solar absorptivity for polished copper?
a) 0.17
b) 0.18
c) 0.19
d) 0.20

Answer: b [Reason:] Solar absorptivity for polished copper depends on frequency and wavelength of the radiation.

4. Which one is having lowest value of solar absorptivity?
a) Snow
b) Red brick
c) Aluminum foil
d) Polished aluminum

Answer: d [Reason:] Solar absorptivity for polished aluminum is 0.09 while that of red brick, aluminum foil and snow are 0.63, 0.15 and 0.28 respectively.

5. What is the value of solar absorptivity for polished stainless steel?
a) 0.37
b) 0.36
c) 0.35
d) 0.34

Answer: a [Reason:] There is vibration within the molecules and it can potentially initiate an electromagnetic waves.

6. Which one is having lowest value of solar absorptivity?
a) Black paint
b) Dull stainless steel
c) Concrete
d) White marble

Answer: d [Reason:] Solar absorptivity for white marble is 0.46 while that of black paint, dull stainless steel and concrete are 0.97, 0.50 and 0.60 respectively.

7. What is the value of solar absorptivity for white marble?
a) 0.45
b) 0.46
c) 0.47
d) 0.48

Answer: b [Reason:] It generates and receive electromagnetic waves at the expense of its stored energy.

8. Which one is having highest value of solar absorptivity?
a) Red brick
b) Asphalt
c) Black paint
d) White paint

Answer: c [Reason:] Emissivity of black paint is 0.97 while that of red brick, asphalt and white paint are 0.63, 0.90 and 0.14 respectively.

9. What is the value of solar absorptivity for asphalt?
a) 0.90
b) 0.80
c) 0.70
d) 0.60

Answer: a [Reason:] Energy emitted by asphalt is not continuous but is in the form of quanta.

10. What is the value of solar absorptivity for snow?
a) 0.25
b) 0.26
c) 0.27
d) 0.28

Answer: d [Reason:] Solar absorptivity for snow varies on the nature of its surface and its temperature.

## Set 4

1. The heat energy absorbed by a known area in a fixed time is determined with the help of an instrument called
a) Psychrometer
b) Pyrheliometer
c) Thermometric well
d) Any instrument

Answer: b [Reason:] The effects of absorption by the atmosphere are eliminated by finding the value of the solar constant at various altitudes of the sun on the same day.

2. The observed solar constant S0, the true solar constant S and the angular elevation Z of the sun are related by the expression
a) S0 =S a SEC Z
b) S0 =2 S a SEC Z
c) S0 =3 S a SEC Z
d) S0 =4 S a SEC Z

Answer: a [Reason:] From the straight line graph between log S0 along y-axis and sec Z along x-axis, the intercept log S on the y-axis is found.

3. The value of solar constant varies between
a) 1123 and 1237 W/m2
b) 1345 and 1453 W/m2
c) 1987 and 2346 W/m2
d) 1335 and 1815 W/m2

Answer: d [Reason:] When the sun lies at a mean distance from the earth, the heat flux from the sun to the outer edge of the atmosphere has been found to be 1350 W/m2.

4. The total amount of heat energy received by the sphere of radius r is
a) 2 π R2 S
b) 6 π R2 S
c) 4 π R2 S
d) π R2 S

Answer: c [Reason:] Area of sphere is 4 π R2.

5. Amount of heat energy radiated by unit surface of the sun in the same time workout as
Take, R = mean distance of earth from the sun and r = radius of sun
a) E = π R2 S/4 π R2
b) E = 4 π R2 S/4 π R2
c) E = 4 π R2
d) E = 4 π R2 S

Answer: b [Reason:] It is the ratio of 4 π R2 S to 4 π R2.

6. Temperature of sun can be workout from
a) Wein’s displacement law
b) Stefan-Boltzmann law
c) Kirchhoff’s law
d) All of the Mentioned

Answer: a [Reason:] (Wavelength) MAX T = 2-89 * 10 -3 m K.

7. The temperature of the photosphere, referred to as the effective temperature of the sun, is usually taken as
a) 3000 K
b) 4000 K
c) 5000 K
d) 6000 K

Answer: d [Reason:] The sun consists of a central hot portion surrounded by the photosphere.

8. The approximate distribution of the flow of sun’s energy to the earth’s surface is
a) 53% is reflected back to space
b) 53% is transmitted to the earth
c) 9% is scattered
d) 22% is absorbed in the atmosphere

Answer: c [Reason:] 33% is reflected back to space, 15% is absorbed in the atmosphere and 43% is transmitted to the earth.

9. The solar radiation that is felt at the earth’s surface includes
(i) Direct radiation that has passed through the atmosphere
(ii) Diffuse radiation from the sky
(iii) Absorbed radiation from the water
Identify the correct statement
a) 1 only
b) 1 and 2
c) 1, 2 and 3
d) 2 and 3

Answer: b [Reason:] Option (iii) must be reflected radiation from water.

10. When the sun lies at a mean distance from the earth, the heat flux from the sun to the outer edge of the atmosphere has been found to be
a) 2350 W/m2
b) 3350 W/m2
c) 4350 W/m2
d) 1350 W/m2

Answer: d [Reason:] 47% of this would reach the earth’s surface.

## Set 5

1. What is the value of specific heat for brick in J/kg K?
a) 835
b) 735
c) 635
d) 535

Answer: a [Reason:] It is a block of ceramic materials. It is built to withstand high temperature, but a low thermal conductivity.

2. Which one is having highest value of specific heat?
a) Asphalt
b) Bakelite
c) Chrome brick
d) Fire clay

Answer: b [Reason:] Specific heat of bakelite is 1465 J/kg K while that of asphalt, chrome brick and fire clay are 920 J/kg K, 835 J/kg K and 960 J/kg K respectively.

3. What is the value of specific heat for asphalt in J/kg K?
a) 920
b) 820
c) 720
d) 620

Answer: a [Reason:] Asphalt is a composite material used to surface roads and airports. It is produced by heating the asphalt binder to decrease its viscosity.

4. What is the value of specific heat for Bakelite in J/kg K?
a) 1665
b) 1565
c) 1465
d) 1365

Answer: c [Reason:] It is also known as polyoxybenzylmethylenglycolanhysride. It is a thermosetting phenol formaldehyde resin. Bakelite was used for its electrical non conductivity.

5. Which one is having lowest value of specific heat?
a) Coal
b) Clay
c) Banana
d) Concrete

Answer: d [Reason:] Specific heat of concrete is 880 J/kg K while that of coal, banana and clay are1260 J/kg K, 3350 J/kg K and 890 J/kg K respectively.

6. What is the value of specific heat for coal in J/kg K?
a) 1260
b) 1360
c) 1460
d) 1560

Answer: a [Reason:] The carbon content of coal is around 60% – 80%. The rest is composed of water, air, hydrogen and Sulphur.

7. What is the value of specific heat for cotton in J/kg K?
a) 1600
b) 1500
c) 1400
d) 1300

Answer: d [Reason:] It is also known as polyethylene. These are highly strain resistant and is used as cushioning and insulating materials in pillows.

8. Which one is having highest value of specific heat?
a) Sand
b) Berea
c) Magnesite
d) Limestone

Answer: c [Reason:] Specific heat of magnesite is 1130 J/kg K while that of sand, barea and limestone are 800 J/kg K, 745 J/kg K and 810 J/kg K respectively.

9. What is the value of specific heat for sand in J/kg K?
a) 800
b) 700
c) 600
d) 500

Answer: a [Reason:] There is a weak bonding between the molecules of sand particles due to which it is exposed to high temperature when left free in atmosphere.

10. Which one is having lowest value of specific heat?
a) Ice
b) Pyrex
c) Paraffin
d) Rubber