Heat & Thermodynamics · JEE Main previous year questions

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2019 13 questions

Q522019 · 12 Apr 2019 · Shift 1
Two moles of helium gas is mixed with three moles of hydrogen molecules (taken to be rigid). What is the molar specific heat of mixture at constant volume ? (R = 8.3 J/mol K)
1. A.21.6 J/mol K
2. B.17.4 J/mol K
3. C.15.7 J/mol K
4. D.19.7 J/mol K
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Answer: B
Q542019 · 12 Apr 2019 · Shift 1
When $M_{1}$ gram of ice at $- 1 0^{\circ} C$ (specific heat = $0.5 cal g^{- 1}^{\circ} C^{- 1}$ ) is added to $M_{2}$ gram of water at $5 0^{\circ} C$ , finally no ice is left and the water is at $0^{\circ} C$ . The value of latent heat of ice, in $cal g^{- 1}$ is :
1. A. $\frac{50 M _{2}}{M _{1}} - 5$
2. B. $\frac{50 M _{2}}{M _{1}}$
3. C. $\frac{5 M _{2}}{M _{1}} - 5$
4. D. $\frac{5 M _{1}}{M _{2}} - 50$
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Answer: A
Q382019 · 12 Apr 2019 · Shift 2
One kg of water, at $2 0^{\circ} C$ , heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of $20 Ω$ . The rms voltage in the mains is 200 V. Ignoring heat loss from the kettle, time taken for water to evaporate fully, is close to : [Specific heat of water = $4200 J/(kg^{\circ} C)$ , Latent heat of water = $2260 kJ/kg$ ]
1. A.10 minutes
2. B.22 minutes
3. C.3 minutes
4. D.16 minutes
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Answer: B
Q572019 · 12 Apr 2019 · Shift 2
A Carnot engine has an efficiency of $\frac{1}{6}$ . When the temperature of the sink is reduced by $6 2^{\circ} C$ , its efficiency is doubled. The temperatures of the source and the sink are, respectively
1. A. $9 9^{\circ} C, 3 7^{\circ} C$
2. B. $12 4^{\circ} C, 6 2^{\circ} C$
3. C. $3 7^{\circ} C, 9 9^{\circ} C$
4. D. $6 2^{\circ} C, 12 4^{\circ} C$
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Answer: A
Q502019 · 10 Apr 2019 · Shift 1
n moles of an ideal gas with constant volume heat capcity $C_{V}$ undergo an isobaric expansion by certain volume. The ratio of the work done in the process, to the heat supplied is :
1. A. $\frac{n R}{C _{V} - n R}$
2. B. $\frac{4 n R}{C _{V} - n R}$
3. C. $\frac{4 n R}{C _{V} + n R}$
4. D. $\frac{n R}{C _{V} + n R}$
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Answer: D
Q382019 · 9 Apr 2019 · Shift 2
A massless spring (k = 800 N/m), attached with a mass (500 g) is completely immersed in 1 kg of water. The spring is stretched by 2 cm and released so that it starts vibrating. What would be the order of magnitude of the change in the temperature of water when the vibrations stop completely ? (Assume that the water container and spring receive negligible heat and specific heat of mass = 400 J/kg K, specific heat of water = 4184 J/kg K)
1. A. $1 0^{- 3} K$
2. B. $1 0^{- 1} K$
3. C. $1 0^{- 5} K$
4. D. $1 0^{- 4} K$
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Answer: C
Q472019 · 9 Apr 2019 · Shift 2
The specific heats, $C_{p}$ and $C_{v}$ of a gas of diatomic molecules, A, are given (in units of $J mo l^{- 1} K^{- 1}$ ) by 29 and 22, respectively. Another gas of diatomic molecules, B, has the corresponding values 30 and 21. If they are treated as ideal gases, then :-
1. A.A is rigid but B has a vibrational mode
2. B.A has a vibrational mode but B has none
3. C.A has one vibrational mode and B has two
4. D.Both A and B have a vibrational mode each
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Answer: B
Q542019 · 9 Apr 2019 · Shift 2
1. A. $\frac{θ _{1}}{10} + \frac{9 θ _{2}}{10}$
2. B. $\frac{θ _{2} + θ _{1}}{2}$
3. C. $\frac{θ _{1}}{6} + \frac{5 θ _{2}}{6}$
4. D. $\frac{θ _{1}}{3} + \frac{2 θ _{2}}{3}$
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Answer: A
Q572019 · 9 Apr 2019 · Shift 2
In a conductor, if the number of conduction electrons per unit volume is $8.5 \times 1 0^{28} m^{- 3}$ and mean free time is 25fs (femto second), it's approximate resistivity is :- ( $m_{e} = 9.1 \times 1 0^{- 31} kg$ )
1. A. $1 0^{- 8} Ω m$
2. B. $1 0^{- 7} Ω m$
3. C. $1 0^{- 5} Ω m$
4. D. $1 0^{- 6} Ω m$
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Answer: A
Q412019 · 8 Apr 2019 · Shift 2
1. A.d a b c
2. B.a d b c
3. C.d a c b
4. D.a d c b
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Answer: A
Q342019 · 12 Jan 2019 · Shift 1
A cylinder of radius R is surrounded by a cylindrical shell of inner radius R and outer radius 2R. The thermal conductivity of the material of the inner cylinder is $K_{1}$ and the of the outer cylinder is $K_{2}$ . Assuming no loss of heat, the effective thermal conductivity of the system for heat flowing along the length of the cylinder is :
1. A. $K_{1} + K_{2}$
2. B. $\frac{K _{1} + 3 K _{2}}{4}$
3. C. $\frac{K _{1} + K _{2}}{2}$
4. D. $\frac{2 K _{1} + 3 K _{2}}{5}$
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Answer: B
Q412019 · 11 Jan 2019 · Shift 2
A metal ball of mass $0.1 kg$ is heated upto $50 0^{\circ} C$ and dropped into a vessel of heat capacity $800 JK^{- 1}$ and containing $0.5 kg$ water. The initial temperature of water and vessel is $3 0^{\circ} C$ . What is the approximate percentage increment in the temperature of the water? [Specific Heat Capacities of water and metal are, respectively, $4200 Jkg^{- 1} K^{- 1}$ and $400 Jkg^{- 1} K^{- 1}$ ]
1. A.20%
2. B.25%
3. C.15%
4. D.30%
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Answer: A
Q452019 · 11 Jan 2019 · Shift 2
In a hydrogen like atom, when an electron jumps from the M-shell to the L-shell, the wavelength of emitted radiation is $λ$ . If an electron jumps from N-shell to the L-shell, the wavelength of emitted radiation will be:
1. A. $\frac{25}{16} λ$
2. B. $\frac{27}{20} λ$
3. C. $\frac{16}{25} λ$
4. D. $\frac{20}{27} λ$
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Answer: D