AP Physics Physics: Thermodynamics & Modern Physics 3 — Questions and Answers
Question 1: According to de Broglie's hypothesis, what is the wavelength of a particle with momentum p?
- λ = hp
- λ = h/p (Correct answer)
- λ = p/h
- λ = h²/p
Correct answer: λ = h/p
De Broglie's relation gives the matter wavelength as λ = h/p, where h is Planck's constant.
Question 2: In nuclear fission, when a heavy nucleus splits, the products have:
- Greater total mass than the original nucleus
- Less total mass than the original nucleus (Correct answer)
- The same total mass as the original nucleus
- Greater atomic number than the original nucleus
Correct answer: Less total mass than the original nucleus
Mass-energy equivalence (E=mc²) means the mass defect is converted to kinetic energy of the fragments.
Question 3: A gas expands adiabatically against zero external pressure (free expansion). What is true?
- Temperature increases
- Work is done on the surroundings
- Internal energy changes
- Both Q and W equal zero (Correct answer)
Correct answer: Both Q and W equal zero
In free expansion, no heat is exchanged (adiabatic) and no work is done (P_ext = 0), so Q = W = 0 and ΔU = 0.
Question 4: The Heisenberg Uncertainty Principle states that:
- Electrons cannot exist inside atomic nuclei
- The position and momentum of a particle cannot both be precisely known simultaneously (Correct answer)
- A particle's energy is always uncertain
- Light behaves only as a wave, never a particle
Correct answer: The position and momentum of a particle cannot both be precisely known simultaneously
Heisenberg's principle states Δx·Δp ≥ ℏ/2, meaning precise knowledge of position limits precision of momentum and vice versa.
Question 5: Which process results in a net decrease in entropy of the universe?
- Ice melting at room temperature
- Gas expanding into a vacuum
- Crystallization of a liquid at its freezing point in an isolated system
- No real process can cause a net decrease in entropy of the universe (Correct answer)
Correct answer: No real process can cause a net decrease in entropy of the universe
The Second Law of Thermodynamics prohibits any process from decreasing the total entropy of the universe.
Question 6: In beta-minus decay, a neutron transforms into:
- A proton and an electron only
- A proton, an electron, and an antineutrino (Correct answer)
- A proton, a positron, and a neutrino
- A proton and a gamma ray
Correct answer: A proton, an electron, and an antineutrino
Beta-minus decay: n → p + e⁻ + ν̄_e; the nucleus emits an electron and an electron antineutrino.
Question 7: A heat pump moves 1500 J of heat from a cold reservoir to a hot reservoir by using 500 J of work. What is the COP (coefficient of performance) of this heat pump?
- 0.33
- 2.0
- 3.0 (Correct answer)
- 4.0
Correct answer: 3.0
COP of a heat pump = Q_hot / W = 1500 J / 500 J = 3.0.
AP Physics Physics: Thermodynamics & Modern Physics 3
According to de Broglie's hypothesis, what is the wavelength of a particle with momentum p?