Physics Objective Questions and Answers: Thermodynamics
Explore reliable objective questions for Thermodynamics tailored for JEE learners. Utilizing these Physics multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.
Download Thermodynamics MCQs with Answers
Access the complete set of multiple-choice questions for Thermodynamics below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official JEE textbooks.
Multiple Choice Questions
(a) 2 : 1
(b) 1 : 2
(c) 3 : 1
(d) 1 : 3
Show Answer & Explanation
Answer: (a) 2 : 1
Explanation:
1. \( W_{iaf}=W_{af}=200 \) J (no work from \( i \) to \( a \)), so \( \Delta U_{if}=500-200=300 \) J and \( U_f=400 \) J.
2. \( Q_{bf}=(400-200)+100=300 \) J and \( Q_{ib}=(200-100)+50=150 \) J.
3. Ratio \( =2:1 \).
Teacher's Note:
1. The change in internal energy depends only on the end states.
(a) The change in internal energy in the whole cyclic process is 250\( R \)
(b) The change in internal energy in the process \( CA \) is 700\( R \)
(c) The change in internal energy in the process \( AB \) is \( -350R \)
(d) The change in internal energy in the process \( BC \) is \( -500R \)
Show Answer & Explanation
Answer: (d) The change in internal energy in the process \( BC \) is \( -500R \)
Explanation:
1. \( \Delta U=\tfrac52R\,\Delta T \) for one mole of a diatomic gas.
2. \( BC \): \( \tfrac52R(600-800)=-500R \). Whole cycle: 0; \( CA \): \( -500R \); \( AB \): \( +1000R \).
Teacher's Note:
1. Internal energy is a state function: \( \Delta U=0 \) for a complete cycle.
(a) 2 J
(b) 42 J
(c) 18 J
(d) 58 J
Show Answer & Explanation
Answer: (c) 18 J
Explanation:
1. \( Q=-20 \) J and \( W=-8 \) J.
2. \( \Delta U=Q-W=-20+8=-12 \) J, so \( U_f=30-12=18 \) J.
Teacher's Note:
1. Work done on the gas is negative work by the gas.
(a) zero
(b) 30 kJ
(c) 10 kJ
(d) 20 kJ
Show Answer & Explanation
Answer: (b) 30 kJ
Explanation:
1. Rigid, so \( W=0 \); the heating is electrical work done on the gas, \( \Delta U=I^2Rt \).
2. \( \Delta U=1\times100\times300=30 \) kJ.
Teacher's Note:
1. Joule heating supplies \( I^2Rt \) of energy.
(a) \( p_0V_0 \)
(b) \( \dfrac{13}2p_0V_0 \)
(c) \( \dfrac{11}2p_0V_0 \)
(d) \( 4p_0V_0 \)
Show Answer & Explanation
Answer: (b) \( \dfrac{13}2p_0V_0 \)
Explanation:
1. Heat is absorbed along \( AB \) (isochoric) and \( BC \) (isobaric).
2. \( Q_{AB}=\tfrac32(2p_0V_0-p_0V_0)=\tfrac32p_0V_0 \); \( Q_{BC}=\tfrac52(4p_0V_0-2p_0V_0)=5p_0V_0 \).
3. Total \( =\dfrac{13}2p_0V_0 \).
Teacher's Note:
1. Use \( C_V=\tfrac32R \) and \( C_P=\tfrac52R \) for the monatomic gas.
(a) zero
(b) \( \tfrac12pV \)
(c) \( pV \)
(d) \( 2pV \)
Show Answer & Explanation
Answer: (d) \( 2pV \)
Explanation:
1. Work equals the area of the triangle: \( \tfrac12\times(3V-V)\times(3p-p)=2pV \).
Teacher's Note:
1. Clockwise cycle on a \( p\)-\(V \) diagram means positive work.
(a) \( 3pV \)
(b) zero
(c) \( 9pV \)
(d) \( 6pV \)
Show Answer & Explanation
Answer: (a) \( 3pV \)
Explanation:
1. Area of the triangle \( =\tfrac12\times(3V-V)\times(4p-p)=3pV \).
Teacher's Note:
1. The net work is the enclosed area.
(a) 8.4 kJ
(b) 84 kJ
(c) 2.1 kJ
(d) 4.2 kJ
Show Answer & Explanation
Answer: (a) 8.4 kJ
Explanation:
1. \( \Delta U=mc\Delta T=0.1\times4184\times20=8368 \) J \( \approx8.4 \) kJ.
Teacher's Note:
1. With negligible expansion, no work is done.
(a) zero
(b) \( \tfrac12RT\ln2 \)
(c) \( RT\ln2 \)
(d) \( \tfrac32RT\ln2 \)
Show Answer & Explanation
Answer: (c) \( RT\ln2 \)
Explanation:
1. \( W_{AB}=R(2T-T)=RT \) and \( W_{CD}=R(T-2T)=-RT \).
2. \( W_{BC}=R(2T)\ln\dfrac{2p}{p}=2RT\ln2 \) and \( W_{DA}=RT\ln\dfrac{p}{2p}=-RT\ln2 \).
3. Net \( =RT\ln2 \).
Teacher's Note:
1. The isobaric parts cancel; the isothermal parts leave a net work.
(a) \( \dfrac{T_1T_2(p_1V_1+p_2V_2)}{p_1V_1T_2+p_2V_2T_1} \)
(b) \( \dfrac{p_1V_1T_1+p_2V_2T_2}{p_1V_1+p_2V_2} \)
(c) \( \dfrac{p_1V_1T_2+p_2V_2T_1}{p_1V_1+p_2V_2} \)
(d) \( \dfrac{T_1T_2(p_1V_1+p_2V_2)}{p_1V_1T_1+p_2V_2T_2} \)
Show Answer & Explanation
Answer: (a) \( \dfrac{T_1T_2(p_1V_1+p_2V_2)}{p_1V_1T_2+p_2V_2T_1} \)
Explanation:
1. \( n_1=\dfrac{p_1V_1}{RT_1} \), \( n_2=\dfrac{p_2V_2}{RT_2} \); energy is conserved: \( T=\dfrac{n_1T_1+n_2T_2}{n_1+n_2} \).
2. \( T=\dfrac{p_1V_1+p_2V_2}{\frac{p_1V_1}{T_1}+\frac{p_2V_2}{T_2}}=\dfrac{T_1T_2(p_1V_1+p_2V_2)}{p_1V_1T_2+p_2V_2T_1} \).
Teacher's Note:
1. Total internal energy is the sum \( \propto nT \).
(a) 0.4 J of work is done by the gas from \( A \) to \( B \)
(b) No work is done by the gas from \( B \) to \( C \)
(c) Net work done by the gas in one cycle is 0.2 J
(d) Work is done by the gas in going from \( B \) to \( C \) and on the gas from \( D \) to \( A \)
Show Answer & Explanation
Answer: (d) Work is done by the gas in going from \( B \) to \( C \) and on the gas from \( D \) to \( A \)
Explanation:
1. \( W_{AB}=2\times10^5\times2\times10^{-6}=0.4 \) J; \( W_{CD}=-0.2 \) J; net \( =0.2 \) J.
2. \( BC \) and \( DA \) are isochoric, so no work is done in them; the last statement is false.
Teacher's Note:
1. Isochoric steps do no work.
(a) 6 cal
(b) 16 cal
(c) 66 cal
(d) 14 cal
Show Answer & Explanation
Answer: (a) 6 cal
Explanation:
1. \( \Delta U=50-20=30 \) cal for both paths.
2. \( W_{ibf}=Q-\Delta U=36-30=6 \) cal.
Teacher's Note:
1. \( \Delta U \) is path independent.
(a) \( \Delta Q \)
(b) \( \Delta W \)
(c) \( \Delta Q+\Delta W \)
(d) \( \Delta Q-\Delta W \)
Show Answer & Explanation
Answer: (d) \( \Delta Q-\Delta W \)
Explanation:
1. \( \Delta U=\Delta Q-\Delta W \) depends only on the end states.
Teacher's Note:
1. Heat and work individually depend on the path.
(a) 384 J
(b) 144 J
(c) 276 J
(d) 452 J
Show Answer & Explanation
Answer: (b) 144 J
Explanation:
1. \( nC_P\Delta T=310\Rightarrow C_P=15.5 \) J/mol K.
2. \( C_V=15.5-8.31=7.19 \); \( Q_V=2\times7.19\times10=144 \) J.
Teacher's Note:
1. \( C_P-C_V=R \).
(a) \( 4p_0V_0 \)
(b) \( 6p_0V_0 \)
(c) \( 4.5p_0V_0 \)
(d) \( 2p_0V_0 \)
Show Answer & Explanation
Answer: (b) \( 6p_0V_0 \)
Explanation:
1. \( \Delta U=\tfrac32(p_BV_B-p_AV_A)=\tfrac32(4p_0V_0-p_0V_0)=4.5p_0V_0 \).
2. \( W=\) area under the line \( =\tfrac12(p_0+2p_0)V_0=1.5p_0V_0 \).
3. \( Q=\Delta U+W=6p_0V_0 \).
Teacher's Note:
1. For a monatomic gas \( \Delta U=\tfrac32\Delta(pV) \).
(a) 540 cal
(b) 40 cal
(c) zero
(d) 500 cal
Show Answer & Explanation
Answer: (d) 500 cal
Explanation:
1. \( W=p\Delta V=1.013\times10^5\times1670\times10^{-6}=169 \) J \( =40 \) cal.
2. \( \Delta U=540-40=500 \) cal, which overcomes intermolecular forces.
Teacher's Note:
1. Latent heat splits into expansion work and internal energy change.
(a) 25.2 K
(b) 35 K
(c) 42 K
(d) 70 K
Show Answer & Explanation
Answer: (d) 70 K
Explanation:
1. A is at constant pressure and B at constant volume: \( nC_P(42)=nC_V\Delta T_B \), so \( \Delta T_B=\gamma\times42=70 \) K.
Teacher's Note:
1. Same heat, so \( C_P\Delta T_A=C_V\Delta T_B \).
(a) \( T_f=\tfrac37T_0 \)
(b) \( T_f=\tfrac73T_0 \)
(c) \( T_f=\tfrac32T_0 \)
(d) \( T_f=\tfrac52T_0 \)
Show Answer & Explanation
Answer: (c) \( T_f=\tfrac32T_0 \)
Explanation:
1. Energy conservation: \( \tfrac52RT_0+\tfrac32R\cdot\tfrac73T_0=\left(\tfrac52+\tfrac32\right)RT_f \).
2. \( 6T_0=4T_f\Rightarrow T_f=\tfrac32T_0 \).
Teacher's Note:
1. Nitrogen is diatomic (\( C_V=\tfrac52R \)); helium is monatomic (\( C_V=\tfrac32R \)).
(a) \( \tfrac12pV \)
(b) \( pV \)
(c) \( 2pV \)
(d) \( 4pV \)
Show Answer & Explanation
Answer: (b) \( pV \)
Explanation:
1. Work is the area of the rectangle: \( (2p-p)(2V-V)=pV \).
Teacher's Note:
1. The net work equals the enclosed area.
(a) work done on the gas is \( 0.5\times10^5 \) J
(b) work done by the gas is \( 0.5\times10^5 \) J
(c) work done on the gas is \( 10^5 \) J
(d) work done by the gas is \( 10^5 \) J
Show Answer & Explanation
Answer: (a) work done on the gas is \( 0.5\times10^5 \) J
Explanation:
1. \( \Delta U=8\times10^5-6.5\times10^5=1.5\times10^5 \) J.
2. Second process: \( W=Q-\Delta U=10^5-1.5\times10^5=-0.5\times10^5 \) J, i.e. work is done on the gas.
Teacher's Note:
1. Same end states give the same \( \Delta U \).
(a) \( \dfrac{\gamma-1}{pV} \)
(b) \( pV \)
(c) \( \dfrac{pV}{\gamma-1} \)
(d) \( \dfrac{pV}{\gamma} \)
Show Answer & Explanation
Answer: (c) \( \dfrac{pV}{\gamma-1} \)
Explanation:
1. \( p\Delta V=R\Delta T=pV \), so \( \Delta T=pV/R \).
2. \( \Delta U=C_V\Delta T=\dfrac{R}{\gamma-1}\cdot\dfrac{pV}R=\dfrac{pV}{\gamma-1} \).
Teacher's Note:
1. \( C_V=R/(\gamma-1) \).
(a) 10 J
(b) 70 J
(c) 84 J
(d) 134 J
Show Answer & Explanation
Answer: (a) 10 J
Explanation:
1. \( \Delta U=Q-W=40-30=10 \) J.
Teacher's Note:
1. The state function \( \Delta U \) depends only on \( A \) and \( C \).
(a) Dulong and Petit law
(b) Newton's law of cooling
(c) Wien's law
(d) Stefan's law
Show Answer & Explanation
Answer: (a) Dulong and Petit law
Explanation:
1. The molar heat capacity of solids approaches \( 3R \) at high temperature (Dulong and Petit).
Teacher's Note:
1. It follows from equipartition for 3 oscillator degrees of freedom.
(a) \( \Delta U_1>\Delta U_2 \)
(b) \( \Delta U_1<\Delta U_2 \)
(c) \( \Delta U_1=\Delta U_2 \)
(d) \( \Delta U_1=\Delta U_2=0 \)
Show Answer & Explanation
Answer: (c) \( \Delta U_1=\Delta U_2 \)
Explanation:
1. Internal energy is a state function, so \( \Delta U \) is the same for both paths.
Teacher's Note:
1. Only the work and heat depend on the path.
(a) 62 J
(b) 104 J
(c) 124 J
(d) 208 J
Show Answer & Explanation
Answer: (d) 208 J
Explanation:
1. The balloon expands at constant (atmospheric) pressure.
2. \( Q=nC_P\Delta T=2\times\tfrac52\times8.31\times5=208 \) J.
Teacher's Note:
1. Helium is monatomic: \( C_P=\tfrac52R \).
(a) 1
(b) 1.33
(c) 1.67
(d) 1.4
Show Answer & Explanation
Answer: (b) 1.33
Explanation:
1. \( p^3\propto V^{-4}\Rightarrow pV^{4/3}=\) constant.
2. So \( \gamma=\tfrac43=1.33 \).
Teacher's Note:
1. Adiabatic: \( pV^\gamma=\) constant.
(a) \( -\dfrac98RT_1 \)
(b) \( \dfrac32RT_1 \)
(c) \( \dfrac{15}8RT_1 \)
(d) \( \dfrac92RT_1 \)
Show Answer & Explanation
Answer: (a) \( -\dfrac98RT_1 \)
Explanation:
1. \( n=\dfrac{5.6}{22.4}=0.25 \) mol; \( T_2=T_1\left(\dfrac{5.6}{0.7}\right)^{2/3}=4T_1 \).
2. \( W=-nC_V\Delta T=-0.25\times\tfrac32R\times3T_1=-\dfrac98RT_1 \).
Teacher's Note:
1. Work done on the gas appears as a negative sign.
(a) 0.76 : 1
(b) 1 : 1
(c) 0.66 : 1
(d) 0.86 : 1
Show Answer & Explanation
Answer: (a) 0.76 : 1
Explanation:
1. After the isothermal step: pressure \( 2p \), volume \( V/2 \).
2. Adiabatic back to \( V \): \( p_f=2p\left(\tfrac12\right)^{1.4}=2\times0.38p=0.76p \).
Teacher's Note:
1. Apply \( pV^\gamma=\) constant.
(a) 4
(b) 6
(c) 5
(d) 9
Show Answer & Explanation
Answer: (a) 4
Explanation:
1. \( TV^{\gamma-1} \) constant with \( \gamma=\tfrac75 \): \( a=32^{2/5}=2^2=4 \).
Teacher's Note:
1. \( 32=2^5 \).
(a) volume
(b) temperature
(c) density
(d) total amount of heat
Show Answer & Explanation
Answer: (d) total amount of heat
Explanation:
1. In an adiabatic process no heat enters or leaves, so the total heat exchanged remains zero.
Teacher's Note:
1. Volume, temperature and density can all change.
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Thermodynamics Objective Questions & Solutions for JEE Physics
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FAQs
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