McqMate
Chapters
| 101. |
The function of a condenser in a thermal power plant is....... |
| A. | To act as reservior to receive steam for turbine |
| B. | To condense steam into condensate to be reused again |
| C. | To create vaccum |
| D. | All of the above |
| Answer» D. All of the above | |
| 102. |
A condenser where circulating water flows through tubes which are surrounded by steam,is known as......... |
| A. | Surface condenser |
| B. | Jet condenser |
| C. | Barometric condenser |
| D. | Evaporative condenser |
| Answer» A. Surface condenser | |
| 103. |
The vaccum obtainable in a condenser is dependent upon...... |
| A. | Capacity of ejector |
| B. | Quantity of steam to be handeled |
| C. | Types of condenser used |
| D. | Temperature of cooling water |
| Answer» D. Temperature of cooling water | |
| 104. |
The ratio of actual vaccum to the ideal vaccum in a condenser is called....... |
| A. | Condenser efficiency |
| B. | Vaccum efficiency |
| C. | Boiler efficiency |
| D. | Nozzle efficiency |
| Answer» B. Vaccum efficiency | |
| 105. |
A condenser in a steam power plant is ....... |
| A. | Increases expansion ratio of steam |
| B. | Reduces back pressure of steam |
| C. | Reduces temperature of exhaust steam |
| D. | All of the above |
| Answer» D. All of the above | |
| 106. |
The actual vaccum in a condenser is equal to...... |
| A. | Barometric pressure + actual pressure |
| B. | Barometric pressure - actual pressure |
| C. | Gauge pressure + atmospheric pressure |
| D. | Gauge pressure - atmospheric pressure |
| Answer» B. Barometric pressure - actual pressure | |
| 107. |
According to Dalton’s law, the total pressure of the mixture of gases is equal to |
| A. | greater of the partial pressures of all |
| B. | average of the partial pressures of all |
| C. | sum of the partial pressures of all |
| D. | sum of the partial pressures of all divided by average molecular weight |
| Answer» C. sum of the partial pressures of all | |
| 108. |
At ideal condition of vapour power cycle, reversible constant pressure heat rejection is carried out at |
| A. | boiler |
| B. | turbine |
| C. | condenser |
| D. | feed pump |
| Answer» C. condenser | |
| 109. |
A condenser condenses the steam coming out from___________. |
| A. | Boiler |
| B. | Turbine |
| C. | Economiser |
| D. | Super heater |
| Answer» B. Turbine | |
| 110. |
What is use of the air pumps in the condenser? |
| A. | Remove water |
| B. | Air leaking in the condenser and to maintain the vacuum. |
| C. | Maintain atmospheric pressure and the condenser. |
| D. | Both (a) & (b). |
| Answer» B. Air leaking in the condenser and to maintain the vacuum. | |
| 111. |
What is the correct formula for net work done of reciprocating engine? |
| A. | Wnet = mean effective pressure × clearance volume |
| B. | Wnet = mean effective pressure × total volume of cylinder |
| C. | Wnet = mean effective pressure × displacement volume |
| D. | none of the above |
| Answer» C. Wnet = mean effective pressure × displacement volume | |
| 112. |
Minimum work in compressor is possible when the value of adiabatic index n is equal to |
| A. | 0.75 |
| B. | 1 |
| C. | 1.27 |
| D. | 1.35 |
| Answer» B. 1 | |
| 113. |
Compressed air coming out from a punctured football |
| A. | becomes hotter |
| B. | becomes cooler |
| C. | remains at the same temperature |
| D. | may become hotter or cooler depending upon the humidity of the surrounding air |
| Answer» B. becomes cooler | |
| 114. |
The capacity of a compressor is 5 m /min. 5 m /min refers to |
| A. | standard air |
| B. | free air |
| C. | compressed air |
| D. | compressed air at delivery pressure |
| Answer» B. free air | |
| 115. |
The overall isothermal efficiency of compressor is defined as the ratio of |
| A. | isothermal h.p. to the BHP of motor |
| B. | isothermal h.p. to adiabatic h.p. |
| C. | power to drive compressor to isothermal h.p. |
| D. | work to compress air isothermally to work for actual compression |
| Answer» A. isothermal h.p. to the BHP of motor | |
| 116. |
The- most efficient method of compressing air is to compress it |
| A. | isothermally |
| B. | adiabatically |
| C. | isentropically |
| D. | isochronically |
| Answer» A. isothermally | |
| 117. |
Maximum work is done in compressing air when the compression is |
| A. | isothermal |
| B. | adiabatic |
| C. | polytropic |
| D. | any one of the above |
| Answer» B. adiabatic | |
| 118. |
The pressure and temperature conditions of air at the suction of compressor are |
| A. | pressure sightly less than atmospheric and temperature slightly more than atmospheric. |
| B. | slightly more than atmospheric |
| C. | slightly less than atmospheric |
| D. | pressure slightly more than atmospheric and temperature slightly less than atmospheric |
| Answer» A. pressure sightly less than atmospheric and temperature slightly more than atmospheric. | |
| 119. |
Isothermal compression effeicency can be attained by running the compressor |
| A. | at very high speed |
| B. | at very slow speed |
| C. | at average speed |
| D. | at zero speed |
| Answer» B. at very slow speed | |
| 120. |
The compressor capacity with decrease in suction temperature |
| A. | increases |
| B. | decreases |
| C. | remains unaffected |
| D. | may increase or decrease depending on compressor capacity |
| Answer» A. increases | |
| 121. |
Isothermal compression efficiency, even when running at high speed, can be approached by using |
| A. | multi-stage compression |
| B. | cold water spray |
| C. | both (a) and (b) above |
| D. | fully insulating the cylinder |
| Answer» C. both (a) and (b) above | |
| 122. |
Compression efficiency is compared against |
| A. | ideal compression |
| B. | adiabatic compression |
| C. | isothermal compression |
| D. | isentropic compression |
| Answer» C. isothermal compression | |
| 123. |
Aeroplanes employ following type of compressor |
| A. | radial flow |
| B. | axial flow |
| C. | centrifugal |
| D. | combination of above |
| Answer» B. axial flow | |
| 124. |
Inter cooling in compressors |
| A. | cools the delivered air |
| B. | results in saving of power in compressing a given volume to given pressure |
| C. | is the standard practice for big compressors |
| D. | enables compression in two stages |
| Answer» B. results in saving of power in compressing a given volume to given pressure | |
| 125. |
An ideal air compressor cycle without clearance on p-v diagram can be represented by following processes |
| A. | one adiabatic, two isobaric, and one constant volume |
| B. | two adiabatic and two isobaric |
| C. | two adiabatic, one isobaric and one constant volume |
| D. | one adiabatic, one isobaric and two constant volume |
| Answer» A. one adiabatic, two isobaric, and one constant volume | |
| 126. |
An ideal air compressor cycle with clearance on p-v diagram can be represented by following processes |
| A. | one adiabatic, two isobaric, and one constant volume |
| B. | two adiabatic and two isobaric |
| C. | two adiabatic, one isobaric and one constant volume, |
| D. | one adiabatic, one isobaric and two constant volume |
| Answer» B. two adiabatic and two isobaric | |
| 127. |
The work done per unit mass of air in compression will be least when n is equal to |
| A. | 1 |
| B. | 1.2 |
| C. | 1.3 |
| D. | 1.4 |
| Answer» A. 1 | |
| 128. |
Isothermal compression though most efficient, but is not -practicable because |
| A. | it requires very big cylinder |
| B. | it does not increase pressure much |
| C. | it is impossible in practice |
| D. | compressor has to run at very slow speed to achieve it |
| Answer» D. compressor has to run at very slow speed to achieve it | |
| 129. |
Ratio of indicated H.P. and brake H.P. is known as |
| A. | mechanical efficiency |
| B. | volumetric efficiency |
| C. | isothermal efficiency |
| D. | adiabatic efficiency |
| Answer» A. mechanical efficiency | |
| 130. |
The ratio of work doen per cycle to the swept volume in case of compressor is called |
| A. | compression index |
| B. | compression ratio |
| C. | compressor efficiency |
| D. | mean effective pressure |
| Answer» D. mean effective pressure | |
| 131. |
Cylinder clearance in a compressor should be |
| A. | as large as possible |
| B. | as small as possible |
| C. | about 50% of swept volume |
| D. | about 100% of swept volume |
| Answer» B. as small as possible | |
| 132. |
Ratio of compression is the ratio of |
| A. | gauge discharge pressure to the gauge intake pressure |
| B. | absolute discharge pressure to the absolute intake pressure |
| C. | pressures at discharge and suction corresponding to same temperature |
| D. | stroke volume and clearance volume |
| Answer» B. absolute discharge pressure to the absolute intake pressure | |
| 133. |
Clearance volume in actual reciprocating compressors is essential |
| A. | to accommodate Valves in the cylinder head |
| B. | to provide cushioning effect |
| C. | to attain high volumetric efficiency |
| D. | to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head. |
| Answer» D. to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head. | |
| 134. |
The net work input required for compressor with increase in clearance volume |
| A. | increases |
| B. | decreases |
| C. | remains same |
| D. | increases/decreases depending on compressor capacity |
| Answer» C. remains same | |
| 135. |
Ratio of indicated h.p. to shaft h.p. is known as |
| A. | compressor efficiency |
| B. | isothermal efficiency |
| C. | volumetric efficiency |
| D. | mechanical efficiency |
| Answer» D. mechanical efficiency | |
| 136. |
Volumetric efficiency is |
| A. | the ratio of stroke volume to clearance volume |
| B. | the ratio of the air actually delivered to the amount of piston displacement |
| C. | reciprocal of compression ratio |
| D. | index of compressor performance |
| Answer» B. the ratio of the air actually delivered to the amount of piston displacement | |
| 137. |
Volumetric efficiency of a compressor with clearance volume |
| A. | increases with increase in compression ratio |
| B. | decreases with increase in compression ratio |
| C. | is not dependent upon compression ratio |
| D. | may increase/decrease depending on compressor capacity |
| Answer» B. decreases with increase in compression ratio | |
| 138. |
Volumetric efficiency of a compressor without clearance volume |
| A. | increases with increase in compression ratio |
| B. | decreases with increase in compression ratio |
| C. | is not dependent upon compression ratio |
| D. | may increase/decrease depending on compressor capacity |
| Answer» C. is not dependent upon compression ratio | |
| 139. |
The clearance volume of the air compressor is kept minimum because |
| A. | it allows maximum compression to be achieved |
| B. | it greatly affects volumetric efficiency |
| C. | it results in minimum work |
| D. | it permits isothermal compression |
| Answer» B. it greatly affects volumetric efficiency | |
| 140. |
Which is false statement about multistage compression. |
| A. | Power consumption per unit of air delivered is low |
| B. | Volumetric efficiency is high |
| C. | It is best suited for compression ratios around 7:1 |
| D. | The moisture in air is condensed in the intercooler |
| Answer» B. Volumetric efficiency is high | |
| 141. |
Reciprocating air compressor is best suited for |
| A. | large quantity of air at high pressure |
| B. | small quantity of air at high pressure |
| C. | small quantity of air at low pressure |
| D. | large quantity of air at low pressure |
| Answer» B. small quantity of air at high pressure | |
| 142. |
Rotary compressor is best suited for |
| A. | large quantity of air at high pressure |
| B. | small quantity of air at high pressure |
| C. | small quantity of air at low pressure |
| D. | large quantity of air at low pressure |
| Answer» D. large quantity of air at low pressure | |
| 143. |
After-cooler is used to |
| A. | cool the air |
| B. | decrease the delivery temperature for ease in handling |
| C. | cause moisture and oil vapour to drop out |
| D. | reduce volume |
| Answer» C. cause moisture and oil vapour to drop out | |
| 144. |
The compressor performance at higher altitude compared to sea level will be |
| A. | same |
| B. | higher |
| C. | lower |
| D. | dependent on other factors |
| Answer» C. lower | |
| 145. |
Pick up the wrong statement about advantages of multistage compression |
| A. | better lubrication is possible advantages of multistage |
| B. | more loss of air due to leakage past the cylinder |
| C. | mechanical balance is better |
| D. | air can be cooled perfectly in between |
| Answer» B. more loss of air due to leakage past the cylinder | |
| 146. |
Losses in a centrifugal compressor are due to |
| A. | inlet losses |
| B. | impeller channel losses |
| C. | diffuser losses |
| D. | all of the above |
| Answer» D. all of the above | |
| 147. |
For supplying intermittent small quantity of air at high pressure, following compressor is best suited |
| A. | centrifugal |
| B. | reciprocating |
| C. | axial |
| D. | screw |
| Answer» B. reciprocating | |
| 148. |
For minimum work in multistage compression, assuming same index of compression in all stages |
| A. | work done in first stage should be more |
| B. | work done in subsequent stages should increase |
| C. | work done in subsequent stages should decrease |
| D. | work done in all stages should be equal |
| Answer» D. work done in all stages should be equal | |
| 149. |
Diffuser in a compressor is used to |
| A. | increase velocity |
| B. | make the flow stream-line |
| C. | convert pressure energy into kinetic energy |
| D. | convert kinetic energy into pressure energy |
| Answer» D. convert kinetic energy into pressure energy | |
| 150. |
Phenomenon of choking in compressor means |
| A. | no flow of air |
| B. | fixed mass flow rate regardless of pressure ratio |
| C. | reducing mass flow rate with increase in pressure ratio |
| D. | increased inclination of chord with air steam |
| Answer» B. fixed mass flow rate regardless of pressure ratio | |
| 151. |
Axial flow compressor has the following advantage over centrifugal compressor |
| A. | larger air handling ability per unit frontal area |
| B. | higher pressure ratio per stage |
| C. | aerofoil blades are used |
| D. | higher average velocities |
| Answer» A. larger air handling ability per unit frontal area | |
| 152. |
Rotary compressors are suitable for |
| A. | large discharge at high pressure |
| B. | low discharge at high pressure |
| C. | large discharge at low pressure |
| D. | low discharge at low pressure |
| Answer» C. large discharge at low pressure | |
| 153. |
The vloumetric efficiency of compressor with increase in compression ratio will |
| A. | increase |
| B. | decrease |
| C. | remain same |
| D. | may increase/decrease depending on clearance volume |
| Answer» B. decrease | |
| 154. |
Unit of thermal conductivity in S.I. units is |
| A. | J/m2 sec |
| B. | J/m °K |
| C. | W/m °K |
| D. | (b) and (c) |
| Answer» C. W/m °K | |
| 155. |
Thermal conductivity of solid metals with rise in temperature normally |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | may increase or decrease depending on temperature |
| Answer» B. decreases | |
| 156. |
Heat transfer takes place as per - |
| A. | zeroth law of thermodynamics |
| B. | first law of thermodynamic |
| C. | second law of the thermodynamics |
| D. | Kirchhoff law (e) Stefan's law. |
| Answer» C. second law of the thermodynamics | |
| 157. |
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» A. conduction | |
| 158. |
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 |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» C. radiation | |
| 159. |
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» B. decrease | |
| 160. |
When heat is Transferred by molecular collision, it is referred to as heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | convection and radiation. |
| Answer» B. convection | |
| 161. |
Heat transfer in liquid and gases takes place by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» B. convection | |
| 162. |
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. | all of the above. |
| Answer» D. all of the above. | |
| 163. |
Heat is closely related with |
| A. | liquids |
| B. | energy |
| C. | temperature |
| D. | entropy |
| Answer» C. temperature | |
| 164. |
Metals are good conductors of heat because |
| A. | their atoms collide frequently |
| B. | thier atoms-are relatively far apart |
| C. | they contain free electrons |
| D. | they have high density |
| Answer» A. their atoms collide frequently | |
| 165. |
Thermal conductivity of air with rise in temperature |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | may increase or decrease depending on temperature |
| Answer» A. increases | |
| 166. |
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» D. different temperatures | |
| 167. |
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» D. conduction and convection. | |
| 168. |
In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by |
| A. | hr (time) |
| B. | sqm (area) |
| C. | °C (temperature) |
| D. | cm (thickness) |
| Answer» D. cm (thickness) | |
| 169. |
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 gradient of the body |
| C. | dependent upon the material of the body |
| D. | all of the above. |
| Answer» D. all of the above. | |
| 170. |
Which of the following has least value of conductivity |
| A. | glass |
| B. | water |
| C. | plastic |
| D. | air |
| Answer» D. air | |
| 171. |
Which of the following is expected to have highest thermal conductivity |
| A. | steam |
| B. | solid ice |
| C. | melting ice |
| D. | water |
| Answer» B. solid ice | |
| 172. |
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» D. all of the above | |
| 173. |
Which of the following has maximum value of thermal conductivity |
| A. | aluminium |
| B. | steel |
| C. | brass |
| D. | copper |
| Answer» A. aluminium | |
| 174. |
Heat is transferred by all three modes of transfer (conduction, convection and radiation) in, |
| A. | electric heater |
| B. | steam condenser |
| C. | melting of ice |
| D. | boiler. |
| Answer» D. boiler. | |
| 175. |
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» D. all of the above | |
| 176. |
Thermal conductivity of wood depends on |
| A. | moisture |
| B. | density |
| C. | temperature |
| D. | all of the above |
| Answer» D. all of the above | |
| 177. |
Heat conducted through unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called |
| A. | thermal resistance |
| B. | thermal coefficient |
| C. | temperature gradient |
| D. | thermal conductivity |
| Answer» D. thermal conductivity | |
| 178. |
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» B. lower | |
| 179. |
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» C. is equal to its emissivity | |
| 180. |
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» A. Grashoff number | |
| 181. |
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» A. higher | |
| 182. |
In counter flow heat exchangers |
| A. | both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state |
| B. | both the fluids at inlet are in their hottest state |
| C. | both the fluids .at exit are in their hottest state |
| D. | one fluid is in hottest state and other in coldest state at inlet |
| Answer» B. both the fluids at inlet are in their hottest state | |
| 183. |
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» A. one dimensional cases only | |
| 184. |
All radiations in a black body are |
| A. | reflected |
| B. | partly reflected and partly absorbed |
| C. | transmitted |
| D. | absorbed |
| Answer» D. absorbed | |
| 185. |
According to Kirchoff's law, 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» D. black body | |
| 186. |
The unit of overall coefficient of heat transfer is |
| A. | W/m2 |
| B. | W/°C |
| C. | W/m2 °C |
| D. | W/m °C |
| Answer» C. W/m2 °C | |
| 187. |
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. | cube of absolute temperature. |
| Answer» C. fourth power of absolute temperature | |
| 188. |
The unit of Stefan Boltzmann constant is |
| A. | watt/cm2 °K |
| B. | watt/cm4 °K |
| C. | watt2/cm °K4 |
| D. | watt/cm2 °K4 |
| Answer» D. watt/cm2 °K4 | |
| 189. |
Stefan Boltzmann law is applicable for heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and radiation combined |
| Answer» C. radiation | |
| 190. |
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. | Krichoff's law |
| B. | Stefan's law |
| C. | Wien' law |
| D. | Planck's law |
| Answer» A. Krichoff's law | |
| 191. |
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit |
| A. | temperature |
| B. | thickness |
| C. | area |
| D. | time |
| Answer» D. time | |
| 192. |
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» A. absorptive power | |
| 193. |
40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the absorptivity of surface is |
| A. | 0.45 |
| B. | 0.55 |
| C. | 0.40 |
| D. | 0.75 |
| Answer» A. 0.45 | |
| 194. |
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» D. all of the above | |
| 195. |
The emissive power of a body depends upon its |
| A. | temperature |
| B. | wave length |
| C. | physical nature |
| D. | all of the above |
| Answer» D. all of the above | |
| 196. |
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. | free convection |
| C. | forced convection |
| D. | radiation |
| Answer» D. radiation | |
| 197. |
In regenerative type heat exchanger, heat transfer takes place by |
| A. | direct mixing of hot and cold fluids |
| B. | a complete separation between hot and cold fluids |
| C. | flow of hot and cold fluids alternately over a surface |
| D. | indirect tr |
| Answer» A. direct mixing of hot and cold fluids | |
| 198. |
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» D. absorbs heat radiations of all wave lengths falling on it | |
| 199. |
If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of |
| A. | 3 |
| B. | 81 |
| C. | 9 |
| D. | 27 |
| Answer» B. 81 | |
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