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JEE Physics

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

301 Q 9 Topics Take Test
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Difficulty: All Easy Medium Hard 241–250 of 301
Topics in JEE Physics
Q.241 Easy Thermodynamics
A heat engine operates between two reservoirs at temperatures 500 K and 300 K. What is the maximum theoretical efficiency of this engine?
A 40%
B 60%
C 75%
D 85%
Correct Answer:  A. 40%
EXPLANATION

Maximum efficiency (Carnot efficiency) = 1 - (T_cold/T_hot) = 1 - (300/500) = 1 - 0.6 = 0.4 = 40%

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Q.242 Easy Thermodynamics
A system absorbs 8000 J of heat and its internal energy increases by 5000 J. According to the first law of thermodynamics, what work is done by the system?
A 3000 J
B 13000 J
C 5000 J
D -3000 J
Correct Answer:  A. 3000 J
EXPLANATION

First law: ΔU = Q - W, so W = Q - ΔU = 8000 - 5000 = 3000 J (work done by the system)

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Q.243 Easy Thermodynamics
A thermodynamic system does 600 J of work while 2400 J of heat is supplied to it. What is the change in internal energy?
A 1800 J
B 2400 J
C 3000 J
D 600 J
Correct Answer:  A. 1800 J
EXPLANATION

By first law of thermodynamics: ΔU = Q - W = 2400 - 600 = 1800 J (where W is work done by system)

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Q.244 Easy Thermodynamics
The internal energy of an ideal gas depends only on:
A Temperature and pressure
B Temperature and volume
C Temperature only
D Pressure and volume
Correct Answer:  C. Temperature only
EXPLANATION

For an ideal gas, internal energy U depends only on temperature (U = nC_vT). This is independent of pressure or volume, as shown by kinetic theory.

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Q.245 Easy Thermodynamics
A gas expands adiabatically from state (P₁, V₁, T₁) to state (P₂, V₂, T₂). Which relation is correct for this process?
A P₁V₁^γ = P₂V₂^γ
B T₁V₁^(γ-1) = T₂V₂^(γ-1)
C P₁/T₁ = P₂/T₂
D All of the above
Correct Answer:  D. All of the above
EXPLANATION

For adiabatic process: PV^γ = constant, TV^(γ-1) = constant, and T^γ P^(1-γ) = constant. All three relations are equivalent and correct.

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Q.246 Easy Thermodynamics
A system absorbs 4000 J of heat and does 1500 J of work. Change in internal energy is:
A 2500 J
B 5500 J
C 1500 J
D -2500 J
Correct Answer:  A. 2500 J
EXPLANATION

First law: ΔU = Q - W = 4000 - 1500 = 2500 J (where W is work done by system)

Test
Q.247 Easy Thermodynamics
A Carnot engine operates between 400 K and 300 K. Its maximum efficiency is:
A 25%
B 33.33%
C 50%
D 75%
Correct Answer:  A. 25%
EXPLANATION

Carnot efficiency η = 1 - T_cold/T_hot = 1 - 300/400 = 0.25 = 25%

Test
Q.248 Easy Thermodynamics
The internal energy of an ideal gas depends on:
A Both temperature and volume
B Both temperature and pressure
C Only temperature
D Only pressure
Correct Answer:  C. Only temperature
EXPLANATION

Internal energy U of ideal gas is U = nCᵥT, which depends only on temperature, not on pressure or volume individually

Test
Q.249 Easy Thermodynamics
An ideal gas undergoes adiabatic compression from state (P₁, V₁, T₁) to (P₂, V₂, T₂). Which relation is correct?
A T₁V₁^(γ-1) = T₂V₂^(γ-1)
B T₁V₁^γ = T₂V₂^γ
C P₁V₁ = P₂V₂
D T₁ = T₂
Correct Answer:  A. T₁V₁^(γ-1) = T₂V₂^(γ-1)
EXPLANATION

For adiabatic process: TV^(γ-1) = constant, therefore T₁V₁^(γ-1) = T₂V₂^(γ-1)

Test
Q.250 Easy Thermodynamics
A diatomic ideal gas expands isothermally from volume V₁ to 2V₁. If the initial pressure is P₀, what is the work done by the gas?
A P₀V₁ ln(2)
B 2P₀V₁ ln(2)
C P₀V₁ ln(0.5)
D P₀V₁
Correct Answer:  A. P₀V₁ ln(2)
EXPLANATION

For isothermal process: W = nRT ln(V₂/V₁) = P₁V₁ ln(V₂/V₁) = P₀V₁ ln(2)

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