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.
| 201. |
*$_Log mean temperature difference in case of counter flow compared to parallel flow will be? |
| A. | Same |
| B. | More |
| C. | Less |
| D. | Depends on other factors |
| Answer» C. Less | |
| 202. |
*$_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. | |
| 203. |
*$_The ratio of surface convection resistance to the internal conduction resistance is known as? |
| A. | Grashoff number |
| B. | Biot number |
| C. | Stanton number |
| D. | Prandtl number |
| Answer» C. Stanton number | |
| 204. |
*$_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 | |
| 205. |
*$_Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be? |
| A. | One |
| B. | Two |
| C. | Three |
| D. | Four |
| Answer» D. Four | |
| 206. |
*$_The emissivity for a black body is? |
| A. | 0 |
| B. | 0.5 |
| C. | 0.75 |
| D. | 1 |
| Answer» E. | |
| 207. |
*$_Metals are good conductors of heat because? |
| A. | Their atoms collide frequently |
| B. | Their atoms are relatively far apart |
| C. | They contain free electrons |
| D. | They have high density |
| Answer» B. Their atoms are relatively far apart | |
| 208. |
*$_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 | |
| 209. |
*$_The insulation ability of an insulator with the presence of moisture would? |
| A. | Increase |
| B. | Decrease |
| C. | Remain unaffected |
| D. | May increase/decrease depending on temperature and thickness of insulation |
| Answer» C. Remain unaffected | |
| 210. |
*$_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 = ≈ì√ÖS/k | |
| 211. |
*$_Unit of thermal conductivity in M.K.S. units is? |
| A. | K cal/kg m² °C |
| B. | K cal m/hr m² °C |
| C. | K cal/hr m² °C |
| D. | K calm/hr °C |
| Answer» C. K cal/hr m¬¨‚⧠¬¨‚àûC | |
| 212. |
*$_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 | |
| 213. |
*/*_Heat transfer in liquid and gases takes place by? |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Conduction and convection |
| Answer» C. Radiation | |
| 214. |
*/*_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 | |
| 215. |
*/*_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 | |
| 216. |
*/*_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 | |
| 217. |
*/*_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. | |
| 218. |
*/*_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? |
| A. | First law of thermodynamics |
| B. | Newton's law of cooling |
| C. | Newton's law of heating |
| D. | Stefan's law |
| Answer» C. Newton's law of heating | |
| 219. |
*/*_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. | |
| 220. |
*/*_The expression Q = ρ AT4 is called? |
| A. | Fourier equation |
| B. | Stefan-Boltzmann equation |
| C. | Newton Reichmann equation |
| D. | Joseph-Stefan equation |
| Answer» C. Newton Reichmann equation | |
| 221. |
*/*_According to Prevost theory of heat exchange? |
| A. | It is impossible to transfer heat from low temperature source to t high temperature source |
| B. | Heat transfer by radiation requires no medium |
| C. | All bodies above absolute zero emit radiation |
| D. | Heat transfer in most of the cases takes place by combination of conduction, convection and radiation |
| Answer» D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation | |
| 222. |
*/*_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» B. Nusselt number | |
| 223. |
*/*_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 | |
| 224. |
*/*_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 | |
| 225. |
*/*_The product of Reynolds number and Prandtl number is known as? |
| A. | Stanton number |
| B. | Biot number |
| C. | Peclet number |
| D. | Grashoff number |
| Answer» D. Grashoff number | |
| 226. |
*/*_According to Newton's law of cooling, the heat transfer from a hot body to a cold body is? |
| A. | Directly proportional to the surface area |
| B. | Directly proportional to the difference of temperatures between the two bodies |
| C. | Either (A) or (B) |
| D. | Both (A) and (B) |
| Answer» E. | |
| 227. |
*/*_The energy distribution of an ideal reflector at higher temperatures is largely in the range of? |
| A. | Shorter wavelength |
| B. | Longer wavelength |
| C. | Remain same at all wavelengths |
| D. | Wavelength has nothing to do with it |
| Answer» B. Longer wavelength | |
| 228. |
*/*_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¬¨‚àûC | |
| 229. |
*/*_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 | |
| 230. |
*/*_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. | |
| 231. |
*/*_Heat transfer takes place as per? |
| A. | Zeroth law of thermodynamics |
| B. | First law of thermodynamic |
| C. | Second law of the thermodynamics |
| D. | Kirchoff's law |
| Answer» D. Kirchoff's law | |
| 232. |
_ The transfer of heat by molecular collision is known as$? |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | None of these |
| Answer» C. Radiation | |
| 233. |
_ Depending on the radiating properties, a body will be opaque when$? |
| 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. | |
| 234. |
_ A grey body is one whose absorptivity$? |
| A. | Varies with temperature |
| B. | Varies with wavelength of the incident ray |
| C. | Is equal to its emissivity |
| D. | Does not vary with temperature and. wavelength of the incident ray |
| Answer» D. Does not vary with temperature and. wavelength of the incident ray | |
| 235. |
_ Moisture would find its way into insulation by vapour pressure unless it is prevented by$? |
| A. | High thickness of insulation |
| B. | High vapour pressure |
| C. | Less thermal conductivity insulator |
| D. | A vapour seal |
| Answer» E. | |
| 236. |
_ The critical temperature is the temperature$? |
| A. | Below which a gas does not obey gas laws |
| B. | Above which a gas may explode |
| C. | Below which a gas is always liquefied |
| D. | Above which a gas will never liquefied |
| Answer» E. | |
| 237. |
_ The thermal diffusivities for gases are generally$? |
| 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 | |
| 238. |
_ The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is$? |
| A. | Equal to one |
| B. | Greater than one |
| C. | Less than one |
| D. | Equal to Nusselt number |
| Answer» B. Greater than one | |
| 239. |
_ Kirchhoff's law states that$? |
| 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 | |
| 240. |
_ The concept of overall coefficient of heat transfer is used in heat transfer problems of$? |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Conduction and convection |
| Answer» E. | |
| 241. |
_ Thermal diffusivity of a substance is$? |
| 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. | |
| 242. |
_ The heat transfer by conduction through a thick cylinder (Q) is given by (where T‚ÇÅ = Higher temperature, T‚ÇÇ = Lower temperature, r‚ÇÅ = Inside radius, r‚ÇÇ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)$? |
| A. | Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁) |
| B. | Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)] |
| C. | Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁) |
| D. | Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁) |
| Answer» B. Q = 2.3 log (r‚Äö√á√á/r‚Äö√á√Ö)/[2≈ì√Ñlk (T‚Äö√á√Ö - T‚Äö√á√á)] | |
| 243. |
_ The critical thickness of insulation for a sphere is$? |
| A. | k/h‚ÇÄ |
| B. | 2k/h‚ÇÄ |
| C. | h‚ÇÄ/k |
| D. | h‚ÇÄ/2k |
| Answer» C. h‚Äö√á√Ñ/k | |
| 244. |
_ Pick up the wrong case. Heat flowing from one side to other depends directly on$? |
| A. | Face area |
| B. | Time |
| C. | Thickness |
| D. | Temperature difference |
| Answer» D. Temperature difference | |
| 245. |
_ Which of the following would lead to a reduction in thermal resistance?$? |
| 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. | |
| 246. |
_ 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. This statement is known as$? |
| A. | Wien's law |
| B. | Stefan's law |
| C. | Kirchhoff's law |
| D. | Planck's law |
| Answer» D. Planck's law | |
| 247. |
_ According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to$? |
| A. | Absolute temperature |
| B. | Square of temperature |
| C. | Fourth power of absolute temperature |
| D. | Fourth power of temperature |
| Answer» D. Fourth power of temperature | |
| 248. |
_ Thermal conductivity of water _________ with rise in temperature.$? |
| A. | Remain same |
| B. | Decreases |
| C. | Increases |
| D. | May increase or decrease depending upon temperature |
| Answer» E. | |
| 249. |
_ Thermal conductivity of a material may be defined as the$? |
| 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. | |
| 250. |
_ The use of heat exchangers is made in$? |
| A. | Radiators in automobile |
| B. | Condensers and boilers in steam plants |
| C. | Condensers and evaporators in refrigeration and air conditioning units |
| D. | All of the above |
| Answer» E. | |