Thermodynamics PYQs Set 6 (PDF)

Set 6 of 16 · Questions 151-180 of 459

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Mere Teacher · Previous Year Questions NEET Physics · Thermodynamics · Set 6 (Q151-180)
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151. $For a certain gas the ratio of specific heats is given to be Y = 1.5 . For this gas$ (1) $C_{v} = 3 R / J$ (2) $C_{P} = 3 R / J$ (3) $C_{P} = 5 R / J$ (4) $C_{v} = 5 R / J$ 152. $The temperature of a body is increased from T_{1} = 127^{\circ} C to T_{2} = 227^{\circ} C . The ambient temperature is 27^{\circ} C . The energies emitted per second by the body at T_{1} and T_{2} are E_{1} and E_{2} respectively. The ratio of \frac{E _{2}}{E _{1}} is$ (1) $1.8$ (2) $2.7$ (3) $3.1$ (4) $4.3$ 153. $Cascaded Carnot engine is an arrangement in which heat sink of one engine is source for other. If high temperature for one engine is T_{1}, low temperature for other engine is T_{2} (Assume work done by both engine is same) Calculate lower temperature of first engine.$ (1) $\frac{2 T _{1} T _{2}}{T _{1} + T _{2}}$ (2) $\frac{T _{1} + T _{2}}{2}$ (3) $0$ (4) $T_{1} T_{2}$ 154. $An engine has an efficiency of 0.25 when temperature of sink is reduced by 58°C, if its efficiency is doubled, then the temperature of the source is$ (1) $150°C$ (2) $222°C$ (3) $242°C$ (4) $232°C$ 155. $An engine is supposed to operate between two reservoirs at temperature 727°C and 227°C. The maximum possible efficiency of such an engine is$ (1) $1/2$ (2) $¼$ (3) $3/4$ (4) $1$ 156. $In a Carnot's engine, as the gas absorbs heat energy from the source, then the temperature of the source$ (1) $decreases$ (2) $increases$ (3) $remains constant$ (4) $becomes zero$ 157. $A sample of gas at temperature T is adiabatically expanded to double its volume. Adiabatic constant for the gas is γ = 3/2 . The work done by the gas in the process is: (μ = 1 mole)$ (1) $RT [1 - 22]$ (2) $RT [2 - 2]$ (3) $RT [2 - 2]$ (4) $RT [22 - 1]$ 158. $In a cyclic process, the internal energy of the gas$ (1) $Increases$ (2) $Decreases$ (3) $Remains constant$ (4) $Becomes zero$ 159. $Let η_{1} is the efficiency of an engine at T1 = 447°C and T2 = 147°C while η_{2} is the efficiency at T1 = 947°C and T2 = 47°C. The \frac{η _{1}}{η _{2}} ratio will be:$ (1) $0.41$ (2) $0.56$ (3) $0.73$ (4) $0.70$ 160. $The efficiency of Carnot's engine operating between reservoirs, maintained at temperatures 27° C and -123° C, is$ (1) $50%$ (2) $24%$ (3) $0.75%$ (4) $0.4%$ 161. $A Carnot engine works between 600 K and 300 K. In each cycle of operations, the engine draws 1000joule of energy from the source at 600 K. The efficiency of the engine is -$ (1) $20%$ (2) $50%$ (3) $70%$ (4) $90%$ 162. $176 grams of CO_{2} can change its temperature from 0^{\circ} C to 30^{\circ} C by absorbing 3600 joules of thermal energy. Molar specific heat of CO_{2} in J mol^{- 1} K^{- 1} is$ (1) $30$ (2) $40$ (3) $50$ (4) $60$ 163. $The efficiency of Carnot's engine operating between reservoirs, maintained at temperatures 2 7^{o} C and - 12 3^{o} C, is$ (1) $50%$ (2) $24%$ (3) $0.75%$ (4) $0.4%$ 164. $When the absolute temperature of the source of a Carnot heat engine is increased by 25 %, its efficiency increases by 80 % . The new efficiency of the engine is$ (1) $12 %$ (2) $24 %$ (3) $48 %$ (4) $36 %$ 165. $The ratio of the specific heats \frac{C _{p}}{C _{v}} = Y in terms of degrees of freedom (n) is given by$ (1) $(1 + \frac{2}{n})$ (2) $(1 + \frac{n}{2})$ (3) $(1 + \frac{1}{n})$ (4) $(1 + \frac{n}{3})$ 166. $2 moles of a monatomic gas requires heat energy Q to be heated from 30^{\circ} C to 40^{\circ} C at constant volume. The heat energy required to raise the temperature of 4 moles of a diatomic gas from 28^{\circ} C to 33^{\circ} C at constant volume is$ (1) $2 Q$ (2) $\frac{7 Q}{2}$ (3) $\frac{4 Q}{3}$ (4) $\frac{5 Q}{3}$ 167. $A Cannot engine works between 200ºC and 0ºC. Another Carnot engine works between 0ºC and -200ºC. In both cases the working substance absorbs 4 kilocalories of heat from the source. The efficiency of first engine will be -$ (1) $\frac{100}{473}$ (2) $\frac{200}{473}$ (3) $\frac{200}{273}$ (4) $\frac{273}{373}$ 168. $Consider a two stage Carnot engine. In the first stage heat Q_{1} is absorbed at temperature T and heat Q_{2} is expelled at temperature αT (where α < 1). In the second stage heat Q_{2} is absorbed at temperature αT and heat Q_{3} is expelled at temperature βT (β < α) . The efficiency of the Carnot engine will be$ (1) $1 - α - β$ (2) $1 - α$ (3) $1 - β$ (4) $1 - αβ$ 169. $A polyatomic gas with n degrees offreedom has a mean energy per molecule given by$ (1) $\frac{nkT}{N}$ (2) $\frac{nkT}{2 N}$ (3) $\frac{nkT}{2}$ (4) $\frac{3 kT}{2}$ 170. $A thermally insulated vessel with nitrogen gas at 27^{\circ} C is moving with a velocity of 100 ms^{- 1} . If the vessel is stopped suddenly, then the percentage change in the pressure of the gas is nearly (assume entire loss in KE of the gas is given as heat to gas and R = 8.3 Jmol^{- 1} K^{- 1})$ (1) $1.1$ (2) $0.93$ (3) $0.5$ (4) $2.25$ 171. $A Carnot engine has efficiency of 50%. If the temperature of sink is reduced by 40°C, its efficiency increases by 30%. The temperature of the source will be:$ (1) $166.7K$ (2) $255. IK$ (3) $266.7 K$ (4) $367.7 K$ 172. $Latent heat of vaporization of water is 22.6 \times 10^{5} J / kg . The amount of heat needed to convert 100 kg of water at 100^{\circ} C into vapour at 100^{\circ} C is$ (1) $11.3 \times 10^{5} J$ (2) $11.3 \times 10^{6} J$ (3) $22.6 \times 10^{6} J .$ (4) $22.6 \times 10^{7} J$ 173. $The ratio of the slopes of isothermal and adiabatic curves is$ (1) $1$ (2) $γ$ (3) $\frac{1}{γ}$ (4) $\frac{3}{2}$ 174. $A scientist says that the efficiency of his heat engine which work at source temperature 12 7^{o} C and sink temperature 2 7^{o} C is 26%, then$ (1) $it is impossible$ (2) $it is possible but less probable$ (3) $it is quite probable$ (4) $data are incomplete.$ 175. $An ideal refrigerator has freezer at a temperature of - 13^{\circ} C . The coefficient of performance of the engine is 5. The temperature of the air (to which heat is rejected) is$ (1) $320^{\circ} C$ (2) $39^{\circ} C$ (3) $325 K$ (4) $325^{\circ} C$ 176. $The initial pressure and volume of an ideal gas are P_{0} and V_{0} . The final pressure of the gas when the gas is suddenly compressed to volume \frac{V _{0}}{4} will be: (Given γ = ratio of specific heats at constant pressure and at constant volume.)$ (1) $P_{0} (4)^{γ}$ (2) $4 P_{0}$ (3) $P_{0}$ (4) $P_{0} (4)^{\frac{1}{γ}}$ 177. $An ideal heat engine working between temperature T_{1} and T_{2} has an efficiency η, the new efficiency if both the source and sink temperature are doubled, will be$ (1) $\frac{η}{2}$ (2) $η$ (3) $2 η$ (4) $3 η$ 178. $A Carnot engine, having an efficiency of η = 1/10 as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is$ (1) $99 J$ (2) $90 J$ (3) $1 J$ (4) $100 J$ 179. $Match List - I with List - II. List-I (A) Isobaric (B) Isochoric (C) Adiabatic (D) Isothermal List - II (I) Δ Q = Δ W (II) Δ Q= Δ U (III) Δ Q= zero (IV) Δ Q = Δ U + P Δ V Δ Q= Heat supplied Δ W = Work done by the system Δ U = Change in internal energy P = Pressure of the system Δ V = Change in volume of the system Choose the correct answer from the options given below:$ (1) $(A)-(IV), (B)-(I), (C)-(III), (D)-(II)$ (2) $(A)-(IV), (B)-(II), (C)-(III), (D)-(I)$ (3) $(A)-(IV), (B)-(III), (C)-(II), (D)-(I)$ (4) $(A)-(II), (B)-(IV), (C)-(III), (D)-(I)$ 180. $A thermally insulated vessel contains an ideal gas of molecular mass M and ratio of specific heats 1.4. Vessel is moving with speed v and is suddenly brought to rest. Assuming no heat is lost to the surrounding and vessel temperature of the gas increases by: (R = universal gas constant)$ (1) $\frac{M v ^{2}}{7 R}$ (2) $\frac{M v ^{2}}{5 R}$ (3) $2 \frac{M v ^{2}}{7 R}$ (4) $7 \frac{M v ^{2}}{5 R}$