Modern Physics practice quiz

Key ideaA photon’s energy is E = hf = hc/λ. Higher frequency means more energy per photon; brighter light means more photons.

Common mistakeThinking brighter light means more energetic photons.

Key ideaK_max = hf − φ, where φ is the work function. Electrons are emitted only above the threshold frequency, however bright the light.

Common mistakeThinking increasing the intensity increases the electrons’ maximum kinetic energy. It increases the number of electrons.

Key ideaA photon emitted or absorbed carries exactly the energy difference between two levels, so the spectrum is discrete lines.

Common mistakeUsing the energy of a single level instead of the difference between two.

Key ideaMatter has a de Broglie wavelength λ = h/p, so a larger momentum means a shorter wavelength.

Common mistakeThinking only light has wave behavior, or that a faster or heavier particle has a longer wavelength. Larger momentum means a shorter wavelength.

Key ideaIn a decay, the nucleon number and charge are conserved. After each half-life, half of the remaining nuclei are left.

Common mistakeThinking all the nuclei decay after two half-lives. A quarter remain.