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Thermal Physics & Thermodynamics (Physics) Solved Questions & Notes (2026) - Apex Rankers

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Thermal Physics & Thermodynamics

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Q. 1 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
What is the theoretical maximum efficiency of a Carnot heat engine operating between a hot reservoir at T_H and a cold reservoir at T_C (in Kelvin)?
A
eta = 1 - (T_C / T_H)
✓ Correct
B
eta = 1 - (T_H / T_C)
C
eta = T_H / T_C
D
eta = (T_H - T_C) / T_C
💡 Step-by-Step Explanation & Concept Rationale
The Carnot efficiency is the absolute thermodynamic upper limit for any heat engine: eta = (T_H - T_C) / T_H = 1 - T_C/T_H.
Q. 2 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In an adiabatic process involving an ideal gas, which thermodynamic variable remains zero?
A
Heat transfer (dQ = 0)
✓ Correct
B
Work done (dW = 0)
C
Change in internal energy (dU = 0)
D
Change in temperature (dT = 0)
💡 Step-by-Step Explanation & Concept Rationale
An adiabatic process is thermally insulated from the surroundings such that no heat enters or leaves the system (Q = 0).
Q. 3 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
According to the Second Law of Thermodynamics, what happens to the total entropy of an isolated system during an irreversible spontaneous process?
A
It always increases (dS > 0)
✓ Correct
B
It decreases to zero
C
It remains strictly constant
D
It fluctuates unpredictably
💡 Step-by-Step Explanation & Concept Rationale
The Second Law dictates that the entropy of an isolated system never decreases and strictly increases in all natural spontaneous irreversible processes.
Q. 4 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
At what angle of projection with the horizontal is the range of a projectile maximum?
A
30 degrees
B
90 degrees
C
45 degrees
✓ Correct
D
60 degrees
💡 Step-by-Step Explanation & Concept Rationale
Range R = (v^2 * sin(2*theta)) / g. The maximum value occurs when sin(2*theta) = 1, giving theta = 45 degrees.
Q. 5 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
Which of the following is a non-conservative force?
A
Frictional force
✓ Correct
B
Gravitational force
C
Electrostatic force
D
Elastic spring force
💡 Step-by-Step Explanation & Concept Rationale
Friction is a non-conservative force because work done depends on the path taken and energy is dissipated as heat.
Q. 6 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In classical mechanics problem #15: In an elastic collision in one dimension between two identical masses where one is initially at rest, what occurs after collision?
A
Both bounce back with equal speeds
B
Both masses stick together and move with half velocity
C
The incident mass stops and target mass moves with original velocity
✓ Correct
D
Both stop immediately
💡 Step-by-Step Explanation & Concept Rationale
For elastic collision of identical masses in 1D, velocities are completely exchanged upon impact (v1' = 0, v2' = v1).
Q. 7 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In classical mechanics problem #21: In an elastic collision in one dimension between two identical masses where one is initially at rest, what occurs after collision?
A
The incident mass stops and target mass moves with original velocity
✓ Correct
B
Both masses stick together and move with half velocity
C
Both bounce back with equal speeds
D
Both stop immediately
💡 Step-by-Step Explanation & Concept Rationale
For elastic collision of identical masses in 1D, velocities are completely exchanged upon impact (v1' = 0, v2' = v1).
Q. 8 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In classical mechanics problem #27: In an elastic collision in one dimension between two identical masses where one is initially at rest, what occurs after collision?
A
Both bounce back with equal speeds
B
Both masses stick together and move with half velocity
C
The incident mass stops and target mass moves with original velocity
✓ Correct
D
Both stop immediately
💡 Step-by-Step Explanation & Concept Rationale
For elastic collision of identical masses in 1D, velocities are completely exchanged upon impact (v1' = 0, v2' = v1).
Q. 9 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In classical mechanics problem #33: In an elastic collision in one dimension between two identical masses where one is initially at rest, what occurs after collision?
A
The incident mass stops and target mass moves with original velocity
✓ Correct
B
Both masses stick together and move with half velocity
C
Both bounce back with equal speeds
D
Both stop immediately
💡 Step-by-Step Explanation & Concept Rationale
For elastic collision of identical masses in 1D, velocities are completely exchanged upon impact (v1' = 0, v2' = v1).
Q. 10 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
What happens to the pressure inside a fluid when its velocity increases according to Bernoulli's theorem?
A
Pressure remains constant
B
Pressure increases
C
Pressure decreases
✓ Correct
D
Pressure becomes negative
💡 Step-by-Step Explanation & Concept Rationale
Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure.
Q. 11 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In fluid mechanics concept #10: What is the ratio of inertial forces to viscous forces in fluid flow analysis?
A
Reynolds Number (Re)
✓ Correct
B
Mach Number
C
Froude Number
D
Prandtl Number
💡 Step-by-Step Explanation & Concept Rationale
The Reynolds number (Re = rho*v*L/mu) is the dimensionless parameter quantifying the ratio of inertial to viscous forces.
Q. 12 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In fluid mechanics concept #16: What is the ratio of inertial forces to viscous forces in fluid flow analysis?
A
Froude Number
B
Mach Number
C
Reynolds Number (Re)
✓ Correct
D
Prandtl Number
💡 Step-by-Step Explanation & Concept Rationale
The Reynolds number (Re = rho*v*L/mu) is the dimensionless parameter quantifying the ratio of inertial to viscous forces.
Q. 13 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In fluid mechanics concept #22: What is the ratio of inertial forces to viscous forces in fluid flow analysis?
A
Reynolds Number (Re)
✓ Correct
B
Mach Number
C
Froude Number
D
Prandtl Number
💡 Step-by-Step Explanation & Concept Rationale
The Reynolds number (Re = rho*v*L/mu) is the dimensionless parameter quantifying the ratio of inertial to viscous forces.
Q. 14 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In fluid mechanics concept #28: What is the ratio of inertial forces to viscous forces in fluid flow analysis?
A
Froude Number
B
Mach Number
C
Reynolds Number (Re)
✓ Correct
D
Prandtl Number
💡 Step-by-Step Explanation & Concept Rationale
The Reynolds number (Re = rho*v*L/mu) is the dimensionless parameter quantifying the ratio of inertial to viscous forces.
Q. 15 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
For an ideal gas undergoing an isothermal expansion, the change in internal energy (delta U) is:
A
Zero
✓ Correct
B
Positive
C
Negative
D
Equal to heat added
💡 Step-by-Step Explanation & Concept Rationale
Internal energy of an ideal gas depends solely on temperature. In an isothermal process, delta T = 0, so delta U = 0.
Q. 16 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In thermodynamic analysis #10: What is the molar specific heat ratio (gamma = Cp/Cv) for a standard monoatomic ideal gas?
A
1.33 (4/3)
B
1.40 (7/5)
C
1.67 (5/3)
✓ Correct
D
2.00
💡 Step-by-Step Explanation & Concept Rationale
For a monoatomic gas with 3 degrees of freedom, Cp = 5/2 R, Cv = 3/2 R, so gamma = 5/3 ≈ 1.67.
Q. 17 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In thermodynamic analysis #16: What is the molar specific heat ratio (gamma = Cp/Cv) for a standard monoatomic ideal gas?
A
1.67 (5/3)
✓ Correct
B
1.40 (7/5)
C
1.33 (4/3)
D
2.00
💡 Step-by-Step Explanation & Concept Rationale
For a monoatomic gas with 3 degrees of freedom, Cp = 5/2 R, Cv = 3/2 R, so gamma = 5/3 ≈ 1.67.
Q. 18 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In thermodynamic analysis #22: What is the molar specific heat ratio (gamma = Cp/Cv) for a standard monoatomic ideal gas?
A
1.33 (4/3)
B
1.40 (7/5)
C
1.67 (5/3)
✓ Correct
D
2.00
💡 Step-by-Step Explanation & Concept Rationale
For a monoatomic gas with 3 degrees of freedom, Cp = 5/2 R, Cv = 3/2 R, so gamma = 5/3 ≈ 1.67.
Q. 19 Physics (Secondary & College Level)
Difficulty: MEDIUM (1 Mark)
In thermodynamic analysis #28: What is the molar specific heat ratio (gamma = Cp/Cv) for a standard monoatomic ideal gas?
A
1.67 (5/3)
✓ Correct
B
1.40 (7/5)
C
1.33 (4/3)
D
2.00
💡 Step-by-Step Explanation & Concept Rationale
For a monoatomic gas with 3 degrees of freedom, Cp = 5/2 R, Cv = 3/2 R, so gamma = 5/3 ≈ 1.67.
Q. 20 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
Young's double-slit experiment demonstrates which fundamental optical wave phenomenon?
A
Total internal reflection
B
Photoelectric effect
C
Interference
✓ Correct
D
Compton scattering
💡 Step-by-Step Explanation & Concept Rationale
Young's double-slit experiment demonstrates constructive and destructive wave interference resulting in alternating bright and dark fringes.
Q. 21 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In wave theory #10: What is the time period T of a simple pendulum of length L in a gravitational field g?
A
2 * pi * sqrt(L / g)
✓ Correct
B
2 * pi * sqrt(g / L)
C
pi * sqrt(L * g)
D
2 * pi * (L / g)^2
💡 Step-by-Step Explanation & Concept Rationale
The period of oscillation for a simple pendulum for small angles is T = 2*pi*sqrt(L/g).
Q. 22 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In wave theory #16: What is the time period T of a simple pendulum of length L in a gravitational field g?
A
pi * sqrt(L * g)
B
2 * pi * sqrt(g / L)
C
2 * pi * sqrt(L / g)
✓ Correct
D
2 * pi * (L / g)^2
💡 Step-by-Step Explanation & Concept Rationale
The period of oscillation for a simple pendulum for small angles is T = 2*pi*sqrt(L/g).
Q. 23 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In wave theory #22: What is the time period T of a simple pendulum of length L in a gravitational field g?
A
2 * pi * sqrt(L / g)
✓ Correct
B
2 * pi * sqrt(g / L)
C
pi * sqrt(L * g)
D
2 * pi * (L / g)^2
💡 Step-by-Step Explanation & Concept Rationale
The period of oscillation for a simple pendulum for small angles is T = 2*pi*sqrt(L/g).
Q. 24 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In wave theory #28: What is the time period T of a simple pendulum of length L in a gravitational field g?
A
pi * sqrt(L * g)
B
2 * pi * sqrt(g / L)
C
2 * pi * sqrt(L / g)
✓ Correct
D
2 * pi * (L / g)^2
💡 Step-by-Step Explanation & Concept Rationale
The period of oscillation for a simple pendulum for small angles is T = 2*pi*sqrt(L/g).
Q. 25 Physics (Secondary & College Level)
Difficulty: EASY (1 Mark)
In wave theory #34: What is the time period T of a simple pendulum of length L in a gravitational field g?
A
2 * pi * sqrt(L / g)
✓ Correct
B
2 * pi * sqrt(g / L)
C
pi * sqrt(L * g)
D
2 * pi * (L / g)^2
💡 Step-by-Step Explanation & Concept Rationale
The period of oscillation for a simple pendulum for small angles is T = 2*pi*sqrt(L/g).
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