MCQOPTIONS
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MCQOPTIONS
This section includes 362 Mcqs, each offering curated multiple-choice questions to sharpen your Mechanical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
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» B. Two dimensional cases only | |
| 102. |
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | None of these |
| Answer» C. Radiation | |
| 103. |
If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called |
| A. | Absorptive power |
| B. | Emissive power |
| C. | Emissivity |
| D. | None of these |
| Answer» C. Emissivity | |
| 104. |
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Conduction and convection |
| Answer» B. Convection | |
| 105. |
Sensible heat is the heat required to |
| A. | Change vapour into liquid |
| B. | Change liquid into vapour |
| C. | Increase the temperature of a liquid of vapour |
| D. | Convert water into steam and superheat it |
| Answer» D. Convert water into steam and superheat it | |
| 106. |
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» E. | |
| 107. |
The value of Prandtl number for air is about |
| A. | 0.1 |
| B. | 0.3 |
| C. | 0.7 |
| D. | 1.7 |
| Answer» D. 1.7 | |
| 108. |
The ratio of surface convection resistance to the internal conduction resistance is known as |
| A. | Grashoff number |
| B. | Biot number |
| C. | Stanton number |
| D. | Prandtl number |
| Answer» C. Stanton number | |
| 109. |
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» E. | |
| 110. |
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is |
| A. | h₁ + h₂ + h₃ |
| B. | (h₁.h₂.h₃)1/3 |
| C. | 1/h₁ + 1/h₂ + 1/h₃ |
| D. | None of these |
| Answer» D. None of these | |
| 111. |
An ordinary passenger aircraft requires a cooling system of capacity. |
| A. | 2 TR |
| B. | 4 TR |
| C. | 8 TR |
| D. | 10 TR |
| Answer» D. 10 TR | |
| 112. |
Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity) |
| A. | RN = hl/k |
| B. | RN = μ cp/k |
| C. | RN = ρ V l /μ |
| D. | RN = V²/t.cp |
| Answer» D. RN = V²/t.cp | |
| 113. |
A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100°C and leaves at 60°C. A cold fluid enters the heat exchanger at 40°C. The mean temperature difference between the two fluids is |
| A. | 20°C |
| B. | 40°C |
| C. | 60°C |
| D. | 66.7°C |
| Answer» B. 40°C | |
| 114. |
In a shell and tube heat exchanger, baffles are provided on the shell side to |
| A. | Improve heat transfer |
| B. | Provide support for tubes |
| C. | Prevent stagnation of shell side fluid |
| D. | All of these |
| Answer» E. | |
| 115. |
Fourier's law of heat conduction gives the heat flow for |
| A. | Irregular surfaces |
| B. | Nonuniform temperature surfaces |
| C. | One dimensional cases only |
| D. | Two dimensional cases only |
| Answer» D. Two dimensional cases only | |
| 116. |
The thermal diffusivities for gases are generally |
| A. | More than those for liquids |
| B. | Less than those for liquids |
| C. | More than those for solids |
| D. | Dependent on the viscosity |
| Answer» B. Less than those for liquids | |
| 117. |
Heat is closely related with |
| A. | Liquids |
| B. | Energy |
| C. | Temperature |
| D. | Entropy |
| Answer» D. Entropy | |
| 118. |
Thermal conductivity of water in general with rise in temperature |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease depending on temperature |
| Answer» E. | |
| 119. |
Thermal conductivity of non-metallic amorphous solids with decrease in temperature |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease depending on temperature |
| Answer» C. Remain constant | |
| 120. |
The critical temperature is the temperature |
| A. | Below which a gas does not obey gas laws |
| B. | Above which a gas may explode |
| C. | Below which a gas is always liquefied |
| D. | Above which a gas will never liquefied |
| Answer» E. | |
| 121. |
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to |
| A. | Absolute temperature |
| B. | T2 |
| C. | T5 |
| D. | T |
| Answer» E. | |
| 122. |
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of |
| A. | 0.002 |
| B. | 0.02 |
| C. | 0.01 |
| D. | 0.1 |
| Answer» C. 0.01 | |
| 123. |
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» E. | |
| 124. |
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» B. Their atoms are relatively far apart | |
| 125. |
Kirchhoff's law states that |
| A. | The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature |
| B. | The wave length corresponding to the maximum energy is proportional to the absolute temperature |
| C. | The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body |
| D. | None of the above |
| Answer» D. None of the above | |
| 126. |
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of |
| A. | 3 |
| B. | 9 |
| C. | 270 |
| D. | 81 |
| Answer» E. | |
| 127. |
The emissivity for a black body is |
| A. | 0 |
| B. | 0.5 |
| C. | 0.75 |
| D. | 1 |
| Answer» E. | |
| 128. |
The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is |
| A. | Equal to one |
| B. | Greater than one |
| C. | Less than one |
| D. | Equal to Nusselt number |
| Answer» B. Greater than one | |
| 129. |
The value of the wavelength for maximum emissive power is given by |
| A. | Wien’s law |
| B. | Planck's law |
| C. | Stefan's law |
| D. | Fourier's law |
| Answer» B. Planck's law | |
| 130. |
The value of the wave length for maximum emissive power is given by |
| A. | Kirchhoff’s law |
| B. | Stefan’s law |
| C. | Wine’s law |
| D. | Planck’s law |
| Answer» D. Planck’s law | |
| 131. |
Thermal conductivity of solid metals with rise in temperature normally |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease depending on temperature |
| Answer» C. Remain constant | |
| 132. |
Pick up the wrong case. Heat flowing from one side to other depends directly on |
| A. | Face area |
| B. | Time |
| C. | Thickness |
| D. | Temperature difference |
| Answer» D. Temperature difference | |
| 133. |
Cork is a good insulator because it has |
| A. | Free electrons |
| B. | Atoms colliding frequency |
| C. | Low density |
| D. | Porous body |
| Answer» E. | |
| 134. |
The insulation ability of an insulator with the presence of moisture would |
| A. | Increase |
| B. | Decrease |
| C. | Remain unaffected |
| D. | May increase/decrease depending on temperature and thickness of insulation |
| Answer» C. Remain unaffected | |
| 135. |
Thermal diffusivity of a substance is |
| A. | Directly proportional to the thermal conductivity |
| B. | Inversely proportional to density of substance |
| C. | Inversely proportional to specific heat |
| D. | All of the above |
| Answer» E. | |
| 136. |
The heat of sun reaches to us according to |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | None of these |
| Answer» D. None of these | |
| 137. |
Emissivity of a white polished body in comparison to a black body is |
| A. | Higher |
| B. | Lower |
| C. | Same |
| D. | Depends upon the shape of body |
| Answer» C. Same | |
| 138. |
The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit) |
| A. | tm = (Δt1 - Δt2)/ loge (Δt1/Δt2) |
| B. | tm = loge (Δt1/Δt2)/ (Δt1 - Δt2) |
| C. | tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2) |
| D. | tm = loge (Δt1 - Δt2)/ Δt1/Δt2 |
| Answer» B. tm = loge (Δt1/Δt2)/ (Δt1 - Δt2) | |
| 139. |
An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be |
| A. | 25 mm |
| B. | 40 mm |
| C. | 160 mm |
| D. | 800 mm |
| Answer» B. 40 mm | |
| 140. |
The concept of overall coefficient of heat transfer is used in heat transfer problems of |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Conduction and convection |
| Answer» E. | |
| 141. |
The natural convection air cooled condensers are used in |
| A. | Domestic refrigerators |
| B. | Water coolers |
| C. | Room air conditioners |
| D. | All of these |
| Answer» E. | |
| 142. |
Fouling factor is used |
| A. | In heat exchanger design as a safety factor |
| B. | In case of Newtonian fluids |
| C. | When a liquid exchanges heat with a gas |
| D. | None of the above |
| Answer» B. In case of Newtonian fluids | |
| 143. |
Unit of thermal conductivity in M.K.S. units is |
| A. | K cal/kg m² °C |
| B. | K cal m/hr m² °C |
| C. | K cal/hr m² °C |
| D. | K calm/hr °C |
| Answer» C. K cal/hr m² °C | |
| 144. |
The critical thickness of insulation for a sphere is |
| A. | k/h₀ |
| B. | 2k/h₀ |
| C. | h₀/k |
| D. | h₀/2k |
| Answer» C. h₀/k | |
| 145. |
Free convection flow depends on |
| A. | Density |
| B. | Coefficient of viscosity |
| C. | Gravitational force |
| D. | All of these |
| Answer» E. | |
| 146. |
Which of the following has maximum value of thermal conductivity? |
| A. | Aluminium |
| B. | Steel |
| C. | Brass |
| D. | Copper |
| Answer» B. Steel | |
| 147. |
The most commonly used method for the design of duct size is the |
| A. | Velocity reduction method |
| B. | Equal friction method |
| C. | Static regains method |
| D. | Dual or double method |
| Answer» D. Dual or double method | |
| 148. |
Thermal diffusivity is a |
| A. | Function of temperature |
| B. | Physical property of a substance |
| C. | Dimensionless parameter |
| D. | All of these |
| Answer» C. Dimensionless parameter | |
| 149. |
Film coefficient is defined as Inside diameter of tube |
| A. | Equivalent thickness of film |
| B. | Thermal conductivity Equivalent thickness of film Specific heat × Viscosity |
| C. | Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity |
| D. | Film coefficient × Inside diameter Thermal conductivity |
| Answer» C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity | |
| 150. |
The emissive power of a body depends upon its |
| A. | Temperature |
| B. | Wave length |
| C. | Physical nature |
| D. | All of the above |
| Answer» E. | |