Heat & Thermodynamics · JEE Main previous year questions

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2020 18 questions

Q372020 · 6 Sept 2020 · Shift 1
1. A. $4 : 1 : 0$
2. B. $2 : 1 : 0$
3. C. $0 : 1 : 2$
4. D. $0 : 1 : 4$
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Answer: B
Q372020 · 6 Sept 2020 · Shift 2
1. A. $K_{1} : K_{3} = 2 : 3, K_{2} : K_{3} = 2 : 5$
2. B. $K_{1} < K_{2} < K_{3}$
3. C. $K_{1} : K_{2} = 5 : 2, K_{1} : K_{3} = 3 : 5$
4. D. $K_{1} > K_{2} > K_{3}$
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Answer: A
Q502020 · 6 Sept 2020 · Shift 2· Numerical answer
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Answer: 19
Q432020 · 3 Sept 2020 · Shift 1
1. A. $\frac{3}{2} R T$
2. B. $\frac{9}{2} R T$
3. C. $\frac{5}{2} R T$
4. D.3RT
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Answer: D
Q432020 · 3 Sept 2020 · Shift 2
A calorimeter of water equivalent 20 g contains 180 g of water at $2 5^{\circ} C$ . 'm' grams of steam at $10 0^{\circ} C$ is mixed in it till the temperature of the mixture is $3 1^{\circ} C$ . The value of 'm' is close to : (Latent heat of water $= 540 cal g^{- 1}$ , specific heat of water $= 1 cal g^{- 1}^{\circ} C^{- 1}$ )
1. A.2.6
2. B.2
3. C.4
4. D.3.2
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Answer: B
Q502020 · 3 Sept 2020 · Shift 2· Numerical answer
If minimum possible work is done by a refrigerator in converting 100 grams of water at $0^{\circ} C$ to ice, how much heat (in calories) is released to the surroundings at temperature $2 7^{\circ} C$ (Latent heat of ice = 80 Cal/gram) to the nearest integer ?
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Answer: 8791
Q462020 · 2 Sept 2020 · Shift 1· Numerical answer
An engine takes in 5 moles of air at $2 0^{\circ} C$ and $1 atm$ , and compresses it adiabatically to $1/1 0^{th}$ of the original volume. Assuming air to be a diatomic ideal gas made up of rigid molecules, the change in its internal energy during this process comes out to be $X kJ$ . The value of $X$ to the nearest integer is ____.
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Answer: 46
Q442020 · 2 Sept 2020 · Shift 2
A heat engine is involved with exchange of heat of 1915 J, – 40J, + 125 J and –Q J, during one cycle achieving an efficiency of 50.0%. The value of Q is
1. A.980 J
2. B.40 J
3. C.400 J
4. D.640 J
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Answer: A
Q322020 · 9 Jan 2020 · Shift 1
Consider two ideal diatomic gases A and B at some temperature T. Molecules of the gas A are rigid, and have a mass m. Molecules of the gas B have an additional vibrational mode, and have a mass $\frac{m}{4}$ . The ratio of the specific heats ( $C_{V}^{A}$ and $C_{V}^{B}$ ) of gas A and B, respectively is :
1. A. $7 : 9$
2. B. $5 : 7$
3. C. $3 : 5$
4. D. $5 : 9$
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Answer: B
Q392020 · 9 Jan 2020 · Shift 1
1. A.
2. B.
3. C.
4. D.
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Answer: B
Q462020 · 9 Jan 2020 · Shift 2· Numerical answer
Starting at temperature 300 K, one mole of an ideal diatomic gas ( $γ = 1.4$ ) is first compressed adiabatically from volume $V_{1}$ to $V_{2} = \frac{V _{1}}{16}$ . It is then allowed to expand isobarically to volume $2 V_{2}$ . If all the processes are the quasi-static then the final temperature of the gas (in $^{\circ} K$ ) is (to the nearest integer) _______.
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Answer: 1818 to 1819
Q342020 · 8 Jan 2020 · Shift 1
1. A.
2. B.
3. C.
4. D.
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Answer: A
Q382020 · 8 Jan 2020 · Shift 2
Consider a mixture of n moles of helium gas and 2n moles of oxygen gas (molecules taken to be rigid) as an ideal gas. Its $C_{p} / C_{v}$ value will be :
1. A.23/15
2. B.67/45
3. C.40/27
4. D.19/13
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Answer: D
Q452020 · 8 Jan 2020 · Shift 2
A carnot engine having an efficiency of $\frac{1}{10}$ is being used as a refrigerator. If the work done on the refrigerator is 10 J, the amount of heat absorbed from the reservoir at lower temperature is :
1. A.90 J
2. B.99 J
3. C.1 J
4. D.100 J
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Answer: A
Q452020 · 7 Jan 2020 · Shift 1
A litre of dry air at STP expands adiabatically to a volume of 3 litres. If $γ = 1.40$ , the work done by air is : ( $3^{1.4} = 4.6555$ ) [Take air to be an ideal gas]
1. A. $60.7 J$
2. B. $100.8 J$
3. C. $90.5 J$
4. D. $48 J$
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Answer: C
Q502020 · 7 Jan 2020 · Shift 1· Numerical answer
A Carnot engine operates between two reservoirs of temperatures 900 K and 300 K. The engine performs 1200 J of work per cycle. The heat energy (in J) delivered by the engine to the low temperature reservoir, in a cycle, is _______.
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Answer: 600
Q322020 · 7 Jan 2020 · Shift 2
Under an adiabatic process, the volume of an ideal gas gets doubled. Consequently the mean collision time between the gas molecule changes from $τ_{1}$ to $τ_{2}$ . If $\frac{C _{p}}{C _{v}} = γ$ for this gas then a good estimate for $\frac{τ _{2}}{τ _{1}}$ is given by :
1. A. $(2)^{\frac{1 + γ}{2}}$
2. B.2
3. C. $(\frac{1}{2})^{\frac{1 + γ}{2}}$
4. D. $(\frac{1}{2})^{γ}$
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Answer: A
Q442020 · 7 Jan 2020 · Shift 2
Two ideal Carnot engines operate in cascade (all heat given up by one engine is used by the other engine to produce work) between temperature, $T_{1}$ and $T_{2}$ . The temperature of the hot reservoir of the first engine is $T_{1}$ and the temperature of the cold reservoir of the second engine is $T_{2}$ . T is temperature of the sink of first engine which is also the source for the second engine. How is T related to $T_{1}$ and $T_{2}$ , if both engines perform equal amount of work?
1. A. $T = \frac{2 T _{1} T _{2}}{T _{1} + T _{2}}$
2. B. $T = T_{1} T_{2}$
3. C. $T = \frac{T _{1} + T _{2}}{2}$
4. D. $T = 0$
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Answer: C