Wave-Particle Duality, Photoelectric Effect, and Atomic Spectra

A set of flashcards reviewing Huygens' principle, wave-particle duality, the photoelectric effect, and related atomic spectra concepts.

What is Huygens' principle?

Every point on a wavefront acts as a new source of circular waves; the next wavefront forms where these secondary waves interfere constructively, and the process repeats.

How is the next wavefront determined in Huygens' principle?

By the locus where secondary waves from all points on the current wavefront interfere constructively.

What evidence shows light behaves as a wave?

Interference and diffraction patterns (e.g., the double-slit experiment).

What evidence shows light behaves as a particle?

Photoelectric effect; light consists of photons that carry quantized energy.

Define a photon.

A quantum of electromagnetic energy; the particle aspect of light with energy E = h f.

What is the relation between photon energy and frequency?

E_photon = h f.

What is Planck's constant value?

h ≈ 6.63 × 10^-34 J·s.

What is the work function?

The minimum energy required to remove an electron from a metal surface (Φ).

What symbol denotes the work function?

Φ (phi).

What is the threshold frequency?

The minimum frequency of incident radiation needed to overcome the work function and eject electrons.

What is the photoelectric effect?

Emission of electrons from a metal when illuminated; depends on photon energy relative to the work function.

What is the relation between photon energy, work function, and maximum KE of photoelectrons?

Ephoton = Φ + KEmax; hence KE_max = h f − Φ.

What is the De Broglie wavelength for matter waves?

λ = h / p, where p is momentum.

How is momentum related to De Broglie wavelength?

p = h / λ; increasing momentum decreases wavelength.

What is the photon energy in terms of wavelength?

E = h c / λ (equivalently E = h f).

What does the KE_max vs frequency graph look like?

A straight line with slope h and intercept −Φ; KE_max = h f − Φ.

How does intensity affect photoelectric emission above threshold?

Increasing intensity increases the number of emitted electrons (more photons per unit time).

What happens if frequency is below threshold, regardless of intensity?

No electron emission occurs.

What is 1 eV in joules?

1 eV = 1.6 × 10^-19 J.

What does the Hydrogen absorption spectrum show?

Absorption lines occur at frequencies corresponding to energy differences between levels; ΔE = h f.

What is excitation energy?

Energy required to move an electron from a lower to a higher energy level.

What is de-excitation energy?

Energy released when an excited electron falls to a lower level, emitted as photons with specific frequencies.

What is the De Broglie wavelength for electrons and how is it derived?

λ = h / p with p = mv; thus λ = h / (m v).

What does electron diffraction demonstrate?

Electrons show diffraction patterns, confirming wave-like behavior at atomic scales.