Thermodynamics PYQs Set 7 (PDF)

Set 7 of 16 · Questions 181-210 of 459

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Mere Teacher · Previous Year Questions NEET Physics · Thermodynamics · Set 7 (Q181-210)
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181. $The temperature of sink of Carnot engine is 2 7^{o} C . Efficiency of engine is 25%. Then temperature of source is$ (1) $22 7^{o} C$ (2) $32 7^{o} C$ (3) $12 7^{o} C$ (4) $2 7^{o} C$ 182. $A sample of 1 mole gas at temperature T is adiabatically expanded to double its volume. If adiabatic constant for the gas is γ = \frac{3}{2}, then the work done by the gas in the process is:$ (1) $\frac{R}{T} [2 - 2]$ (2) $\frac{T}{R} [2 + 2]$ (3) $RT [2 - 2]$ (4) $RT [2 + 2]$ 183. $In a thermodynamic system Δ U represents the increase in its internal energy and dW is the work done by the system then correct statement out of the following is$ (1) $Δ U = dW is an isothermal process$ (2) $Δ U = - dW is an adiabatic process$ (3) $Δ U = - dW is an isothermal process$ (4) $Δ U = dW is an adiabatic process.$ 184. $A thermocol box has a total wall area (including the lid) of 1.0 m^{2} and wall thickness of 3 cm . It is filled with ice at 0^{\circ} C . If the average temperature outside the box is 30^{\circ} C throughout the day, the amount of ice that melts in one day is [Use K_{thermocol} = 0.03 W / mK, L_{fusion (ice)} = 3.00 \times 10^{5} J / kg]$ (1) $1 kg$ (2) $2.88 kg$ (3) $25.92 kg$ (4) $8.64 kg$ 185. $The relation between absolute temperature (T) and pressure (P) of a gas in an adiabatic process is$ (1) $p^{γ} T^{1 - γ} = constant$ (2) $p^{1 - γ} T^{γ} = constant$ (3) $p^{γ - 1} T^{γ} = constant$ (4) $p^{γ} T^{γ - 1} = constant$ 186. $A carnot engine whose efficiency is 40 %, receives heat at 500 K . If the efficiency is to be 50 %, the source temperature for the same exhaust temperature is$ (1) $900 K$ (2) $600 K$ (3) $700 K$ (4) $800 K$ 187. $A rod is found to be 0.05 cm longer at 40^{\circ} C than it is at 10^{\circ} C . The length of the rod at 0^{\circ} C is (coefficient of linear expansion of the material of the rod = 1.5 \times 10^{- 5} ° C^{- 1})$ (1) $101.1 cm$ (2) $120.2 cm$ (3) $105.1 cm$ (4) $111.1 cm$ 188. $1 g of water of volume 1 cm^{3} at 100^{\circ} C is converted into steam at same temperature under normal atmospheric pressure = (= 1 \times 10^{5} Pa) . The volume of steam formed equals 1671 cm^{3} . If the specific latent heat of vaporisation of water is 2256 J / g, the change in internal energy is [NEET 2019]$ (1) $2423 J$ (2) $2089 J$ (3) $167 J$ (4) $2256 J$ 189. $An ideal gas heat engine operates in Carnot cycle between 227°C and 127°C. It absorbs 6 \times 1 0^{4} cals of heat at higher temperature. Amount of heat converted to work is$ (1) $2.4 \times 1 0^{4} cal$ (2) $6 \times 1 0^{4} cal$ (3) $1.2 \times 1 0^{4} cal$ (4) $4.8 \times 1 0^{4} cal$ 190. $1 g of water at 100^{\circ} C is completely converted into stream at 100^{\circ} C . 1. g of steam occupies a volume of 1650 cc . (Neglect the volume of 1 g of water at 100^{\circ} C). At the pressure of 10^{5} N / m^{2}, latent heat of steam is 540 cals / g ( 1 calorie = 4.2 joule ). The increase in the internal energy (in joule) is$ (1) $2310$ (2) $2103$ (3) $1650$ (4) $2150$ 191. $A carnot engine works between ice point and steam point. It is desired to increase efficiency by 20%, by changing temperature of sink to -$ (1) $253 K`$ (2) $293 K$ (3) $303 K$ (4) $243 K$ 192. $In thermodynamic processes which of the following statements is not true?$ (1) $In an isochoric process pressure remains constant.$ (2) $In an isothermal process the temperature remains constant.$ (3) $In an adiabatic process P V^{γ} = constant.$ (4) $In an adiabatic process the system is insulated from the surroundings.$ 193. $The temperature inside a refrigerator is t_{2}^{o} C and the room temperature is t_{1}^{o} C . The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be$ (1) $\frac{t _{1}}{t _{1} - t _{2}}$ (2) $\frac{t _{1} + 273}{t _{1} - t _{2}}$ (3) $\frac{t _{2} + 273}{t _{1} - t _{2}}$ (4) $\frac{t _{1} + t _{2}}{t _{1} + 273}$ 194. $A diatomic gas (γ = 1.4) does 100 J of work in an isobaric expansion. The heat given to the gas is:$ (1) $250 J$ (2) $150 J$ (3) $350 J$ (4) $490 J$ 195. $A 210 W heater is used to heat 100 g water. The time required to raise the temperature of this water from 25^{\circ} C to 100^{\circ} C is (specific heat capacity of water = 4200 J / Kg -^{\circ} C)$ (1) $100 s$ (2) $125 s$ (3) $150 s$ (4) $200 s$ 196. $A sample of gas at temperature T is adiabatically expanded to double its volume. The work done by the gas in the process is (given, γ = \frac{3}{2})$ (1) $W = TR (2 - 2)$ (2) $W = \frac{T}{R} (2 - 2)$ (3) $W = \frac{R}{T} (2 - 2)$ (4) $W = RT (2 - 2)$ 197. $The mean free path of molecules of a gas, (radius r) is inversely proportional to$ (1) $r^{3}$ (2) $r^{2}$ (3) $r$ (4) $r$ 198. $Two metal rods A and B each of length 50 cm and diameter 4.0 mm are joined together at temperature 30^{\circ} C . What is the change in length of the combined rod at 230^{\circ} C ? [Given linear expansion coefficients of rods A and B are respectively, 2.0 \times 10^{- 5} /° C and (1.0 \times 10^{- 5} /° C)$ (1) $4 mm$ (2) $2 mm$ (3) $3 mm$ (4) $1 mm$ 199. $310 J of heat is required to raise the temperature of 2 moles of an ideal gas at constant pressure from 25^{\circ} C to 35^{\circ} C . The amount of heat required to raise the temperature of the gas through the same range at constant volume is$ (1) $384 J$ (2) $144 J$ (3) $276 J$ (4) $452 J$ 200. $The emissivity of a perfect black body is increased to 16 times by increasing its temperature. If the initial temperature is T, then final temperature of that black body is$ (1) $4 T$ (2) $8 T$ (3) $2 T$ (4) $16 T$ 201. $During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its temperature. The ratio of \frac{C _{p}}{C _{v}} for the gas is$ (1) $\frac{5}{3}$ (2) $\frac{3}{2}$ (3) $\frac{4}{3}$ (4) $2$ 202. $A Carnot engine takes 300 calories of heat from a source at 500 K and rejects 150 calories of heat to the sink. The temperature of the sink is$ (1) $125 K$ (2) $250 K$ (3) $750 K$ (4) $1000 K$ 203. $A monatomic gas at pressure P_{1} and volume V_{1} is compressed adiabatically to 1/8th of its original volume. What is the final pressure of the gas?$ (1) $64 P_{1}$ (2) $P_{1}$ (3) $16 P_{1}$ (4) $32 P_{1}$ 204. $A sphere of surface area 4 m^{2} at temperature 400 K and having emissivity 0.5 is located in an environment of temperature 200 K . The net rate of energy exchange of the sphere is (Stefan Boltzmann constant σ = 5.67 \times 10^{- 8} Wm^{- 2} K^{4})$ (1) $3260.8 W$ (2) $1632.4 W$ (3) $2721.6 W$ (4) $4216.4 W$ 205. $Relation between pressure (P) and energy (E) of a gas is$ (1) $P = \frac{2}{3} E$ (2) $P = \frac{1}{3} E$ (3) $P = E$ (4) $P = 3 E$ 206. $In a Carnot's engine, as the gas gives heat energy to the sink, then the temperature of the sink$ (1) $increases$ (2) $decreases$ (3) $remains constant$ (4) $becomes zero$ 207. $If a carnot engine is working between steam point and ice point, then its efficiency will be$ (1) $24.9 %$ (2) $25.7%$ (3) $26.8%$ (4) $28.8%$ 208. $The focal length of a spherical mirror made of steel is 150 cm . If the temperature of the mirror increases by 200 K, its focal length become (coefficient of linear expansion of steel α = 12 \times 10^{- 6} ° C^{- 1} .)$ (1) $186.3 cm$ (2) $153.6 cm$ (3) $150.036 cm$ (4) $150.36 cm$ 209. $Find the ratio of the length of a steel rod and a copper rod if the steel rod is 4 cm longer than the copper rod at any temperature. [The coefficient of linear expansion for steel and copper are 1.1 \times 10^{- 5} /° C and 1.7 \times 10^{- 5} /° C respectively]$ (1) $\frac{17}{11}$ (2) $\frac{11}{17}$ (3) $\frac{11}{4}$ (4) $\frac{17}{4}$ 210. $A Carnot’s engine is made to work between 200°C and 0°C first and then between 0°C and -200°C. The ratio of efficiencies of the engine in the two cases is$ (1) $1.73 : 1$ (2) $1 : 1.73$ (3) $1 : 1$ (4) $1 : 2$