Physics: Thermodynamics & Modern Physics Flashcards

The mass defect of a nucleus is directly related to its:

Answer: Binding energy

Binding energy = mass defect × c²; the mass defect represents the energy needed to completely separate the nucleus into its constituent nucleons.

Which of the following correctly describes the relationship between absolute temperature T and the average kinetic energy of molecules in an ideal gas?

Answer: KE_avg = (3/2)kT

From the kinetic theory of ideal gases, the average translational kinetic energy per molecule is (3/2)k_B T.

Alpha particles are deflected significantly by electric and magnetic fields because they:

Answer: Carry a charge of +2e

Alpha particles consist of 2 protons and 2 neutrons, giving them a charge of +2e, which causes deflection in fields.

A refrigerator removes 800 J of heat from a cold interior and expels 1100 J to the warm exterior. How much work does the refrigerator's compressor do?

Answer: 300 J

By energy conservation: W = Q_hot - Q_cold = 1100 J - 800 J = 300 J of work input required.

What happens to the wavelength of a photon when it passes through a gravitational field (gravitational redshift)?

Answer: It increases as it escapes a gravitational well

Photons lose energy climbing out of a gravitational well, decreasing frequency and increasing wavelength — this is gravitational redshift.

In nuclear fusion reactions in the sun, four hydrogen nuclei ultimately combine to produce:

Answer: A helium-4 nucleus, two positrons, and two neutrinos

The proton-proton chain net reaction: 4¹H → ⁴He + 2e⁺ + 2ν_e + energy (as gamma rays).

A process is thermodynamically reversible if:

Answer: It occurs infinitely slowly and the system remains in equilibrium throughout

A reversible process is a quasi-static idealization where the system passes through a continuous series of equilibrium states with no entropy generation.