A charged particle is accelerated through a potential difference of 100V. Its de Broglie wavelength is λ₁. If accelerated through 400V, the wavelength becomes λ₂. The ratio λ₁/λ₂ is:

The correct answer is B: 2. λ = h/√(2mKE). Since KE ∝ V, λ ∝ 1/√V. Therefore λ₁/λ₂ = √(400/100) = √4 = 2

A moving charge experiences a magnetic force. This force is always:

The correct answer is B: Perpendicular to both velocity and magnetic field. Magnetic force is given by F = q(v × B), which is the cross product of velocity and field. Cross product is always perpendicular to both vectors.

In a tunnel diode, the negative resistance region occurs due to:

The correct answer is B: Quantum mechanical tunneling through the bandgap. At low forward bias, electrons tunnel through the narrow bandgap, creating peak current. As voltage increases, direct band-to-band current dominates, causing current to decrease with voltage (negative differential resistance).

According to the uncertainty principle, if the position of an electron is known with uncertainty Δx = 10⁻¹⁰ m, the minimum uncertainty in momentum is:

The correct answer is A: 5.27 × 10⁻²⁵ kg·m/s. Δx·Δp ≥ h/(4π). Δp ≥ 1.055×10⁻³⁴/(4π×10⁻¹⁰) ≈ 5.27 × 10⁻²⁵ kg·m/s.

What is the capacitance of an isolated conducting sphere of radius R in vacuum?

The correct answer is A: 4πε₀R. The capacitance of an isolated conducting sphere is C = 4πε₀R = R/k, where k = 1/(4πε₀).

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JEE Physics
Thermodynamics

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

27 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 27

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.11 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.12 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)

Test

Q.13 Easy Thermodynamics

A heat pump delivers 5000 J of heat to a house while consuming 1500 J of work. Its coefficient of performance is:

A 3.33

B 2.33

C 4.33

D 1.33

Correct Answer: A. 3.33

EXPLANATION

For heat pump: COP = Q_h/W = 5000/1500 = 3.33. This indicates the pump delivers 3.33 J of heat for every 1 J of work input.

Test

Q.14 Easy Thermodynamics

What is the efficiency of a Carnot engine operating between 400 K and 300 K?

A 25%

B 33.3%

C 50%

D 75%

Correct Answer: A. 25%

EXPLANATION

Carnot efficiency: η = 1 − (T_cold/T_hot) = 1 − (300/400) = 1 − 0.75 = 0.25 = 25%

Test

Q.15 Easy Thermodynamics

An ideal gas undergoes an adiabatic process. If the gas is compressed, which of the following is true?

A Temperature decreases, internal energy decreases

B Temperature increases, internal energy increases

C Temperature remains constant, internal energy increases

D Temperature decreases, internal energy remains constant

Correct Answer: B. Temperature increases, internal energy increases

EXPLANATION

In adiabatic compression (Q = 0), work is done on the gas (W < 0). By first law: ΔU = Q − W = 0 − W > 0. Since ΔU ∝ ΔT for ideal gas, temperature increases.

Test

Q.16 Easy Thermodynamics

A system absorbs 500 J of heat and performs 200 J of work on the surroundings. What is the change in internal energy of the system?

A 300 J

B 700 J

C −300 J

D −700 J

Correct Answer: A. 300 J

EXPLANATION

By first law of thermodynamics: ΔU = Q − W = 500 − 200 = 300 J

Test

Q.17 Easy Thermodynamics

A carnot engine operates between temperatures 500 K and 300 K. What is its maximum efficiency?

A 40%

B 60%

C 83.3%

D 16.7%

Correct Answer: A. 40%

EXPLANATION

Carnot efficiency: η = 1 - (Tc/Th) = 1 - (300/500) = 1 - 0.6 = 0.4 = 40%

Test

Q.18 Easy Thermodynamics

In an adiabatic process, if a gas is compressed, which statement is correct?

A Temperature decreases

B Temperature increases

C Temperature remains constant

D Heat is absorbed from surroundings

Correct Answer: B. Temperature increases

EXPLANATION

In adiabatic compression, no heat exchange occurs (Q=0). Work is done on the gas, so ΔU = W (positive). Since ΔU increases, temperature must increase.

Test

Q.19 Easy Thermodynamics

For one mole of an ideal monatomic gas, the ratio Cp/Cv is:

A 1.40

B 1.67

C 1.33

D 1.50

Correct Answer: B. 1.67

EXPLANATION

For monatomic gas: Cv = (3/2)R and Cp = (5/2)R. Therefore Cp/Cv = (5/2)/(3/2) = 5/3 ≈ 1.67

Test

Q.20 Easy Thermodynamics

A thermodynamic system undergoes a process where internal energy increases by 150 J while the system does 100 J of work on surroundings. What is the heat absorbed by the system?

A 250 J

B 50 J

C -50 J

D 150 J

Correct Answer: A. 250 J

EXPLANATION

By first law: ΔU = Q - W. Here ΔU = 150 J, W = 100 J (work done by system). So Q = ΔU + W = 150 + 100 = 250 J

Test

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