Title 12.THERMODYNAMICS - Questions.pdf ✅

12.THERMODYNAMICS (1.)A Carnot engine has efficiency 1/5. Efficiency becomes 1/3 when temperature of sink is decreased by 50K. What is the temperature of sink? (a.) 325 K (b.) 375 K (c.) 300 K (d.) 350 K (2.)A refrigerator absorbs 2000 cals of heat from ice trays. If the coefficient of performance is 4, then work done by the motor is (a.) 2100 J (b.) 4200 J (c.) 8400 J (d.) 500 J (3.)When the amount of work done is 333 cal and change in internal energy is 167 cal, then the heat supplied is (a.) 166 cal (b.) 333 cal (c.) 500 cal (d.) 400 cal (4.)Carnot cycle (reversible) of a gas represented by a Pressure-Volume curve is shown in the diagram Consider the following statements I. Area ABCD = Work done on the gas II. Area ABCD = Net heat absorbed III. Change in the internal energy in cycle = 0 Which of these are correct (a.) I only (b.) II only (c.) II and III (d.) I, II and III (5.)An ideal gas is heated at constant pressure and absorbs amount of heat Q. If the adiabatic exponent is γ, then the fraction of heat absorbed in raising the internal energy and performing the work, in (a.) 1 − 1 γ (b.) 1 + 1 γ (c.) 1 − 2 γ (d.) 1 + 2 γ (6.)For an adiabatic expansion of a perfect gas, the value of ∆P P is equal to (a.) −√γ ∆V V (b.) − ∆V V (c.) −γ ∆V V (d.) −γ 2 ∆V V (7.)In the following p − V diagram figure two adiabates cut two isothermals at T1 and T2. The value of Vb/Vc is (a.) = Va/Vd (b.) < Va/Vd (c.) > Va/Vd (d.) Cannot say (8.)A gas expands 0.25m3 at constant pressure 103N/m2 , the work done is (a.) 2.5 ergs (b.) 250 J (c.) 250 W (d.) 250 N (9.)Ten moles of an ideal gas at constant temperature 500 K is compressed from 50 L to 5 L. Work done in the process is (Given, R = 8.31 J − mol −1 − K −1 ) (a.) −1.2 × 104 J (b.) −2.4 × 104 J (c.) −4.8 × 104 J (d.) −9.6 × 104 J (10.)If an ideal gas is compressed isothermally then (a.) No work is done against gas (b.) Heat is released by the gas (c.) The internal energy of gas will increase (d.) Pressure does not change (11.)The work done, W during an isothermal process in which 1 mole of the gas expands from an initial volume V1 to a final volume V2 is given by (R=gas constant, T=temperature) (a.) R(V2 − V1 ) loge ( T1 T2 ) (b.) R(T2 − T1 ) loge ( V2 V1 ) (c.) RT loge( V2 V1 ) (d.) 2RT loge ( V1 V2 ) (12.)Two isothermally are shown in figure at temperature T1 and T2. Which of the following relations is correct? A D C B P V
(a.) T1 > T2 (b.) T1 < T2 (c.) T1 = T2 (d.) T1 = 1 2 T2 (13.)In Carnot engine efficiency is 40% at hot reservoir temperature T. For efficiency 50% what will be temperature of hot reservoir? (a.) T 5 (b.) 2T 5 (c.) 6T (d.) 6T 5 (14.)In changing the state of thermodynamics from A to B state, the heat required is Q and the work done by the system is W. The change in its internal energy is (a.) Q + W (b.) Q − W (c.) Q (d.) Q−W 2 (15.)1 cm3 of water at its boiling point absorbs 540 cal of heat to become steam with a volume = 1.013 × 105Nm−2 and the mechanical equivalent of heat = 4.19 Jcal −1 , the energy spend in this process in overcoming intermolecular forces is (a.) 540 cal (b.) 40 cal (c.) 500 cal (d.) Zero (16.)The adiabatic elasticity of hydrogen gas (γ = 1.4) at NTP is (a.) 1 × 105N/m2 (b.) 1 × 10−8N/m2 (c.) 1.4 N/m2 (d.) 1.4 × 105 N/m2 (17.)Which one of the following statements is true in respect of usual quantities represented by ∆Q, ∆U and ∆W (a.) ∆U and ∆W are path dependent (b.) ∆Q and ∆U are path dependent (c.) ∆U does not dependent on path (d.) ∆Q does not depend upon path (18.)In a thermodynamic system working substance is ideal gas, its internal energy is in the form of (a.) Kinetic energy only (b.) Kinetic and potential energy (c.) Potential energy (d.) None of these (19.)Helium at 27°C has a volume of 8 litres. It is suddenly compressed to a volume of 1 litre. The temperature of the gas will be [γ = 5/3] (a.) 108°C (b.) 9327°C (c.) 1200°C (d.) 927°C (20.)For an ideal gas, in an isothermal process (a.) Heat content remains constant (b.) Heat content and temperature remain constant (c.) Temperature remains constant (d.) None of the above (21.)An engineer claims to have made an engine delivering 10 kW power with fuel consumption of 1 g/s. The calorific value of the fuel is 2 kcal/g. Is the claim of the engineer (a.) Valid (b.) Invalid (c.) Depends on engine design (d.) Depends of the load (22.)A graph of pressure versus volume for an ideal gas for different processes is as shown. In the graph curve OC represents (a.) Isochoric process (b.) Isothermal process (c.) Isobaric process (d.) Adiabatic process (23.)For nitrogen Cp − Cv = x and for argon, Cp − Cv = y. The relation between x and y is given by (a.) x = y (b.) x = 7y (c.) y = 7x (d.) x = 1 2 y (24.)If ∆Q and ∆W represent the heat supplied to the system and the work done on the system respectively, then the first law of thermodynamics can be written as Where ∆U is the internal energy (a.) ∆Q = ∆U + ∆W (b.) ∆Q = ∆U − ∆W (c.) ∆Q = ∆W − ∆U (d.) ∆Q = −∆W − ∆U (25.)In an isothermal change, an ideal gas obeys (a.) Boyle’s law (b.) Charle’s law