Heat Transfer PYQs Set 7 (PDF)

Set 7 of 7 · Questions 181-200 of 200

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Mere Teacher · Previous Year Questions NEET Physics · Heat Transfer · Set 7 (Q181-200)
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181. $A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body$ (1) $Radiation$ (2) $Convection$ (3) $Conduction$ (4) $Temperature remains unchanged$ 182. $The velocity of heat radiation in vacuum is$ (1) $Equal to that of light$ (2) $Less than that of light$ (3) $Greater than that of light$ (4) $Equal to that of sound$ 183. $Two materials having coefficients of thermal conductivity \cdot 3 K^{’} and^{’} K^{’} and thickness^{’} d^{’} and ' 3 d', respectively, are joined to form a slab as shown in the figure. The temperatures of the outer surfaces are \cdot^{’} θ_{2}^{’} and^{’} θ_{1}^{’} respectively, (θ_{2} > θ_{1}) . The temperature at the interface is:$ (1) $\frac{θ _{1}}{10} + \frac{9 θ _{2}}{10}$ (2) $\frac{θ _{2} + θ _{1}}{2}$ (3) $\frac{θ _{1}}{6} + \frac{5 θ _{2}}{6}$ (4) $\frac{θ _{1}}{3} + \frac{2 θ _{2}}{3}$ 184. $Three rods of identical cross-section and lengths are made of three different materials of thermal conductivity K_{1}, K_{2} and K_{3} respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at 100^{\circ} C and the other at 0^{\circ} C (see figure). If the joints of the rod are at 70^{\circ} C and 20^{\circ} C in steady state and there is no loss of energy from the surfac of the rod, the correct relationship between K_{1}, K_{2} and K_{3} is$ (1) $K_{1} : K_{3} = 2 : 3, K_{2} : K_{3} = 2 : 5$ (2) $K_{1} < K_{2} < K_{3}$ (3) $K_{1} : K_{2} = 5 : 2, K_{1} : K_{3} = 3 : 5$ (4) $K_{1} > K_{2} > K_{3}$ 185. $Three rods of Copper, brass and steel are welded together to form a Y-shaped structure. Area of cross-section of each rod = 4 c m^{2} . End of copper rod is maintained at 100°C where as ends of brass and steel are kept at 0°C. Lengths of the copper, brass and steel rods are 46, 13 and 12 cm respectively. The rods are thermally insulated from surroundings except at ends. Thermal conductivities of copper, brass and steel are 0.92, 0.26 and 0.12 CGS units respectively. Rate of heat flow through copper rod is:$ (1) $1.2 cal/s$ (2) $2.4 cal/s$ (3) $4.8 cal/s$ (4) $6.0 cal/s$ 186. $The heat capacities of three liquids A, B and C of same volumes are in the ratio 3 : 2 : 1. They are allowed to cool in the same surroundings and in same conditions for the same temperature difference. Which of these will cool first?$ (1) $A$ (2) $B$ (3) $C$ (4) $All will cool in same time$ 187. $There is a black spot on a body. If the body is heated and carried in dark room then it glows more. This can be explained on the basis of$ (1) $Newton’s law of cooling$ (2) $Wien’s law$ (3) $Kirchoff’s law$ (4) $Stefan’s$ 188. $If the temperature of the sun (black body) is doubled, the rate of energy received on earth will be increased by a factor of$ (1) $2$ (2) $4$ (3) $8$ (4) $16$ 189. $Relation between emissivity e and absorptive power a is (for black body)$ (1) $e = a$ (2) $e = \frac{1}{a}$ (3) $e = a^{2}$ (4) $a = e^{2}$ 190. $Heat travels through vacuum by$ (1) $Conduction$ (2) $Convection$ (3) $Radiation$ (4) $Both (a) and (b)$ 191. $Good absorbers of heat are$ (1) $Poor emitters$ (2) $Non-emitters$ (3) $Good emitters$ (4) $Highly polished$ 192. $Infrared radiation is detected by$ (1) $Spectrometer$ (2) $Pyrometer$ (3) $Nanometer$ (4) $Photometer$ 193. $A thermos flask is polished well$ (1) $To make attractive$ (2) $For shining$ (3) $To absorb all radiations from outside$ (4) $To reflect all radiations from outside$ 194. $Pick out the statement which is not true$ (1) $IR radiations are used for long distance photography$ (2) $IR radiations arise due to inner electron transitions in atoms$ (3) $IR radiations are detected by using a bolometer$ (4) $Sun is the natural source of IR radiation$ 195. $If a black body is heated at a high temperature, it seems to be$ (1) $Blue$ (2) $White$ (3) $Red$ (4) $Black$ 196. $When the body has the same temperature as that of surroundings$ (1) $It does not radiate heat$ (2) $It radiates the same quantity of heat as it absorbs$ (3) $It radiates less quantity of heat as it receives from surroundings$ (4) $It radiates more quantity of heat as it receives heat from surroundings$ 197. $How is the temperature of stars determined by$ (1) $Stefan’s law$ (2) $Wein’s displacement law$ (3) $Kirchhoff’s law$ (4) $Ohm’s law$ 198. $A body, which emits radiations of all possible wavelengths, is known as$ (1) $Good conductor$ (2) $Partial radiator$ (3) $Absorber of photons$ (4) $Perfectly black-body$ 199. $At a certain temperature for given wave length, the ratio of emissive power of a body to emissive power of black body in same circumstances is known as$ (1) $Relative emissivity$ (2) $Emissivity$ (3) $Absorption coefficient$ (4) $Coefficient of reflection$ 200. $The value of Stefan’s constant is$ (1) $5.67 \times 1 0^{- 8} W / m^{2} - K^{4}$ (2) $5.67 \times 1 0^{- 5} W / m^{2} - K^{4}$ (3) $5.67 \times 1 0^{- 11} W / m^{2} K^{4}$ (4) $None of these$