AP Physics Physics: Thermodynamics & Modern Physics 4 — Questions and Answers
Question 1: Blackbody radiation peaks at a shorter wavelength when the temperature of the object:
- Decreases
- Increases (Correct answer)
- Remains constant
- Reaches absolute zero
Correct answer: Increases
Wien's displacement law states λ_max = b/T; higher temperature shifts the peak to shorter wavelengths.
Question 2: An ideal gas undergoes an isothermal expansion. Which of the following is true?
- Internal energy increases
- Heat is absorbed by the gas (Correct answer)
- Pressure increases
- Temperature decreases
Correct answer: Heat is absorbed by the gas
In isothermal expansion, ΔU = 0 for an ideal gas, so Q = W > 0; the gas must absorb heat to do work.
Question 3: Which of the following particles carries a charge of +1e and has a mass of approximately 1 atomic mass unit?
- Electron
- Neutron
- Positron
- Proton (Correct answer)
Correct answer: Proton
A proton carries a charge of +1e and has a mass of approximately 1.67 × 10⁻²⁷ kg, or ~1 amu.
Question 4: The photoelectric effect provided evidence that light:
- Travels at a finite speed
- Has wave-like interference properties
- Consists of discrete packets of energy called photons (Correct answer)
- Cannot travel through a vacuum
Correct answer: Consists of discrete packets of energy called photons
The photoelectric effect demonstrated that light energy is quantized into photons, each with energy E = hf.
Question 5: For an isochoric (constant volume) process, the work done by the gas is:
- Equal to the heat added
- Equal to the change in internal energy
- Zero (Correct answer)
- Negative
Correct answer: Zero
At constant volume, ΔV = 0, so W = PΔV = 0; all heat goes into changing internal energy.
Question 6: In Compton scattering, when an X-ray photon collides with a free electron, the scattered photon has:
- The same wavelength as the incident photon
- A shorter wavelength than the incident photon
- A longer wavelength than the incident photon (Correct answer)
- Zero energy
Correct answer: A longer wavelength than the incident photon
The photon transfers some energy to the electron, so the scattered photon has less energy and therefore a longer wavelength.
Question 7: Which quantum number describes the shape of an electron's orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (m_l)
- Spin quantum number (m_s)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number l determines the shape of the orbital (s, p, d, f correspond to l = 0, 1, 2, 3).
AP Physics Physics: Thermodynamics & Modern Physics 4
Blackbody radiation peaks at a shorter wavelength when the temperature of the object: