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.
| 151. |
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity) |
| A. | h = k/ ρS |
| B. | h = ρS/k |
| C. | h = S/ρk |
| D. | h = kρ/S |
| Answer» B. h = ρS/k | |
| 152. |
The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity) |
| A. | Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁) |
| B. | Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)] |
| C. | Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁) |
| D. | Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁) |
| Answer» B. Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)] | |
| 153. |
The amount of radiation mainly depends on |
| A. | Nature of body |
| B. | Temperature of body |
| C. | Type of surface of body |
| D. | All of the above |
| Answer» E. | |
| 154. |
Wien’s law states that the wave length corresponding to ________ is proportional to the absolute temperature. |
| A. | Minimum energy |
| B. | Maximum energy |
| C. | Both (A) and (B) |
| D. | None of these |
| Answer» C. Both (A) and (B) | |
| 155. |
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a |
| A. | Grey body |
| B. | Brilliant white polished body |
| C. | Red hot body |
| D. | Black body |
| Answer» E. | |
| 156. |
The transfer of heat by molecular collision is known as |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | None of these |
| Answer» C. Radiation | |
| 157. |
Heat transfer by radiation mainly depends upon |
| A. | Its temperature |
| B. | Nature of the body |
| C. | Kind and extent of its surface |
| D. | All of the above |
| Answer» E. | |
| 158. |
The thermal diffusivities for solids are generally |
| A. | Less than those for gases |
| B. | Less than those for liquids |
| C. | More than those for liquids and gases |
| D. | More or less same as for liquids and gases |
| Answer» D. More or less same as for liquids and gases | |
| 159. |
Log mean temperature difference in case of counter flow compared to parallel flow will be |
| A. | Same |
| B. | More |
| C. | Less |
| D. | Depends on other factors |
| Answer» C. Less | |
| 160. |
Depending on the radiating properties, a body will be opaque when |
| A. | P = 0, x = 0 and a = 1 |
| B. | P=1, x = 0 and a = 0 |
| C. | P = 0, x = 1 and a = 0 |
| D. | X = 0, a + p = 1 |
| Answer» E. | |
| 161. |
In case of liquids and gases, the heat transfer takes place according to |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | None of these |
| Answer» C. Radiation | |
| 162. |
The heat transfer takes place according to |
| A. | Zeroth law of thermodynamics |
| B. | First law of thermodynamics |
| C. | Second law of thermodynamics |
| D. | Kirchhoff's law |
| Answer» D. Kirchhoff's law | |
| 163. |
In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the |
| A. | Reynold's number |
| B. | Grashoff's number |
| C. | Reynold's number, Grashoff's number |
| D. | Prandtl number, Grashoff's number |
| Answer» E. | |
| 164. |
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» E. | |
| 165. |
The automobile radiator is a heat exchanger of |
| A. | Parallel flow type |
| B. | Counter flow type |
| C. | Cross flow type |
| D. | Regenerator type |
| Answer» D. Regenerator type | |
| 166. |
LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is |
| A. | Higher |
| B. | Lower |
| C. | Same |
| D. | Depends on the area of heat exchanger |
| Answer» B. Lower | |
| 167. |
The ratio of the energy absorbed by the body to total energy falling on it is called |
| A. | Absorptive power |
| B. | Emissive power |
| C. | Absorptivity |
| D. | Emissivity |
| Answer» B. Emissive power | |
| 168. |
Which of the following is the case of heat transfer by radiation? |
| A. | Blast furnace |
| B. | Heating of building |
| C. | Cooling of parts in furnace |
| D. | Heat received by a person from fireplace |
| Answer» E. | |
| 169. |
The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as |
| A. | Emissivity |
| B. | Transmissivity |
| C. | Reflectivity |
| D. | Intensity of radiation |
| Answer» E. | |
| 170. |
Thermal conductivity of wood depends on |
| A. | Moisture |
| B. | Density |
| C. | Temperature |
| D. | All of the above |
| Answer» E. | |
| 171. |
In free convection heat transfer, Nusselt number is function of |
| A. | Grashoff number and Reynold number |
| B. | Grashoff number and Prandtl number |
| C. | Prandtl number and Reynold number |
| D. | Grashoff number, Prandtl number and Reynold number |
| Answer» C. Prandtl number and Reynold number | |
| 172. |
Joule sec is the unit of |
| A. | Universal gas constant |
| B. | Kinematic viscosity |
| C. | Thermal conductivity |
| D. | Planck's constant |
| Answer» E. | |
| 173. |
Heat transfer in liquid and gases takes place by |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Conduction and convection |
| Answer» C. Radiation | |
| 174. |
Which of the following would lead to a reduction in thermal resistance? |
| A. | In conduction, reduction in the thickness of the material and an increase in thermal conductivity. |
| B. | In convection, stirring of the fluid and cleaning the heating surface. |
| C. | In radiation, increasing the temperature and reducing the emissivity. |
| D. | All of the above |
| Answer» E. | |
| 175. |
The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to |
| A. | -1/3 |
| B. | -2/3 |
| C. | 1 |
| D. | -1 |
| Answer» B. -2/3 | |
| 176. |
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» E. | |
| 177. |
The critical radius is the insulation radius at which the resistance to heat flow is |
| A. | Maximum |
| B. | Minimum |
| C. | Zero |
| D. | None of these |
| Answer» C. Zero | |
| 178. |
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to |
| A. | Absolute temperature |
| B. | Square of temperature |
| C. | Fourth power of absolute temperature |
| D. | Fourth power of temperature |
| Answer» D. Fourth power of temperature | |
| 179. |
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by |
| A. | Convection |
| B. | Radiation |
| C. | Forced convection |
| D. | Free convection |
| Answer» C. Forced convection | |
| 180. |
Which of the following property of air does not increase with rise in temperature? |
| A. | Thermal conductivity |
| B. | Thermal diffusivity |
| C. | Density |
| D. | Dynamic viscosity |
| Answer» D. Dynamic viscosity | |
| 181. |
Thermal conductivity of water _________ with rise in temperature. |
| A. | Remain same |
| B. | Decreases |
| C. | Increases |
| D. | May increase or decrease depending upon temperature |
| Answer» E. | |
| 182. |
The rate of energy transferred by convection to that by conduction is called |
| A. | Stanton number |
| B. | Nusselt number |
| C. | Biot number |
| D. | Peclet number |
| Answer» C. Biot number | |
| 183. |
A perfect black body is one which |
| A. | Is black in colour |
| B. | Reflects all heat |
| C. | Transmits all heat radiations |
| D. | Absorbs heat radiations of all wave lengths falling on it |
| Answer» E. | |
| 184. |
Thermal conductivity of a material may be defined as the |
| A. | Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C |
| B. | Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C |
| C. | Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces |
| D. | All of the above |
| Answer» E. | |
| 185. |
Planck’s law holds good for |
| A. | black bodies |
| B. | polished bodies |
| C. | all coloured bodies |
| D. | all of the above |
| Answer» B. polished bodies | |
| 186. |
When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body, |
| A. | α = 1, ρ = 0 and τ = 0 |
| B. | α = 0, ρ = 1 and τ = 0 |
| C. | α = 0, ρ = 0 and τ = 1 |
| D. | α + ρ = 1 and τ = 0 |
| Answer» D. α + ρ = 1 and τ = 0 | |
| 187. |
The amount of heat flow through a body by conduction is |
| A. | Directly proportional to the surface area of the body |
| B. | Directly proportional to the temperature difference on the two faces of the body |
| C. | Dependent upon the material of the body |
| D. | All of the above |
| Answer» E. | |
| 188. |
The radiation emitted by a black body is known as |
| A. | Black radiation |
| B. | Full radiation |
| C. | Total radiation |
| D. | All of these |
| Answer» E. | |
| 189. |
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in |
| A. | Electric heater |
| B. | Steam condenser |
| C. | Boiler |
| D. | Refrigerator condenser coils |
| Answer» D. Refrigerator condenser coils | |
| 190. |
All radiations in a black body are |
| A. | Reflected |
| B. | Refracted |
| C. | Transmitted |
| D. | Absorbed |
| Answer» E. | |
| 191. |
The unit of Stefan-Boltzmann constant is%! |
| A. | Watt/mK |
| B. | Watt/m²K² |
| C. | Watt/m²K4 |
| D. | Watt/mK² |
| Answer» D. Watt/mK¬¨‚⧠| |
| 192. |
The unit of Stefan Boltzmann constant is%! |
| A. | watt/cm² °K |
| B. | watt/cm⁴ °K |
| C. | watt²/cm °K⁴ |
| D. | watt/cm² °K⁴ |
| Answer» E. | |
| 193. |
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a%! |
| A. | Black body |
| B. | Grey body |
| C. | Opaque body |
| D. | White body |
| Answer» B. Grey body | |
| 194. |
Thermal diffusivity is%! |
| A. | A dimensionless parameter |
| B. | Function of temperature |
| C. | Used as mathematical model |
| D. | A physical property of the material |
| Answer» E. | |
| 195. |
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 | |
| 196. |
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 | |
| 197. |
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be%! |
| A. | One |
| B. | Two |
| C. | Three |
| D. | Four |
| Answer» D. Four | |
| 198. |
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 | |
| 199. |
The emissivity for a black body is%! |
| A. | 0 |
| B. | 0.5 |
| C. | 0.75 |
| D. | 1 |
| Answer» E. | |
| 200. |
*$_According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a? |
| A. | Grey body |
| B. | Brilliant white polished body |
| C. | Red hot body |
| D. | Black body |
| Answer» E. | |